Organic Chemistry - Phenols, Aldehydes, Ketones, Carboxylic Acids, Esters, Amines, and Amides
Phenols
Phenols have a hydroxyl group attached to an aromatic ring.
The parent compound is phenol, with the chemical formula , also known as monohydroxybenzene or carbolic acid.
Properties:
Colorless crystalline solid.
Melting point of .
Highly poisonous and causes chemical burns upon skin contact.
More acidic than alcohols and water.
Boiling point is nearly .
Moderately soluble in water and highly combustible.
Common phenols: catechol, resorcinol (m-dihydroxybenzene), and hydroquinone (para-dihydroxybenzene).
Uses:
Disinfectant and antiseptic.
Intermediate in making plastics, explosives, drugs, and dyes.
Antioxidants in foods and applications in herbicides and pesticides.
Specific phenols and uses:
Cresol: bactericides, pesticides, preservatives in some pharmaceuticals, and disinfectants.
Catechol: produce pesticides.
Salicylic acid: treat warts, dandruff, acne, fungal infections (ringworm), and ichthyosis.
Alphanaptol: production of dyes, insecticides, and pharmaceuticals.
Tetrahydrocannabinol: principal active component of marijuana.
Phenolphthalein: indicator in acid-base titrations.
Chemical behavior:
The hydroxyl group activates the aromatic ring toward electrophilic substitution, especially at the ortho and para positions.
Undergoes halogenation and nitration more readily than benzene due to its activation.
Summary: aromatic compounds with a hydroxyl group attached to an aromatic ring, with industrial, medicinal, and biological roles distinguished by acidity, hydrogen bonding, and reactivity on the aromatic ring.
Production: obtained from coal tar; several commercial methods are used to produce phenol synthetically.
Differential Tests for Phenol
Litmus test: Blue litmus paper turns red due to acidity.
Ferric chloride test: Aqueous solution of phenol reacts with freshly prepared ferric chloride, giving a colored complex.
Phenol and resorcinol produce violet or blue.
Catechol produces a green color.
Salicylic acid produces violet.
Alpha naphthol has no specific coloration, but with alcohol, it yields a violet-blue coloration.
Cresol produces a violet or blue color.
Bromine water test: Phenol undergoes electrophilic substitution reaction with bromine. Addition of bromine water produces a brown color that disappears, forming a white precipitate of tribromophenol.
Aldehydes and Ketones
Acetone is the simplest and most common ketone; uses include nail polish remover, paints, varnish, and resins. It is also produced during fat metabolism.
Aldehydes have the carbonyl group at the end of the carbon chain bonded to at least one hydrogen.
Ketones have the carbonyl group within the carbon chain bonded to two carbon atoms.
Key difference: Aldehydes are readily oxidized to carboxylic acid, while ketones resist oxidation under normal conditions. Aldehydes are generally more reactive than ketones due to less steric hindrance and electronic effects.
Aldehydes and Ketones:
Reactive organic chemical compounds.
The word aldehyde is a combination of alcohol and dehydrogenated.
Form carboxylic acids when they are further oxidized.
General formula of aldehyde is RCHO, where R is hydrogen or an alkyl or aryl group (bonded to one hydrogen).
Common names for aldehydes are often derived from the name of the acid that it will form.
Ketones consist of an alkyl chain and a double-bonded oxygen attached to one of the carbon atoms in the chain. In ketones, oxygen is bonded to a secondary or middle-of-the-chain carbon.
Ketones are less chemically active than aldehydes and are used in perfumes and paints to stabilize other ingredients.
Other uses include adhesives, components of thinners, printing inks, cleaning agents, tanning, solvents, preservatives, hydraulic fluids, and as intermediates in the chemical industry.
Acetone, acetoacetate, and beta-hydroxybutyrate are ketones generated from carbohydrates, fatty acids, and amino acids in our bodies.
Ketones are elevated in blood after fasting (including a night of sleep) and during starvation since carbohydrates will be broken down.
Both aldehydes and ketones contain the carbonyl group (carbon-to-oxygen double bond).
Aldehydes have at least one hydrogen bonded to the carbonyl group, whereas ketones have one alkyl or aryl aromatic group bonded to the carbonyl group.
Common names for aliphatic aldehydes are derived from the common names of the carboxylic acids.
The "ic" or "oic acid" ending of the acid name is dropped and replaced with the suffix "aldehyde."
Formaldehyde (one-carbon aldehyde) is derived from formic acid (one-carbon acid).
Acetaldehyde (two-carbon aldehyde) is derived from acetic acid (two-carbon acid).
Aromatic aldehydes containing an aldehyde group bonded to an aromatic ring are named after the corresponding carboxylic acid; benzaldehyde is derived from benzoic acid.
Preparation of Aldehydes and Ketones
Prepared through oxidation of alcohols using an oxidizing agent like potassium dichromate.
Methanol reacts with oxygen in air in the presence of a silver or copper catalyst to form formaldehyde and water.
Methanol + O2 \xrightarrow[Ag \or Cu]{} Formaldehyde + H2O
Properties
Boiling Point: Aldehydes and ketones cannot hydrogen bond to themselves because no hydrogen atom is attached to the oxygen atom of the carbonyl group; they have lower boiling points compared to alcohols.
Solubility: Aldehydes and ketones are about the same solubility as alcohols and ethers. Formaldehyde, acetaldehyde, and acetone are soluble in water, but as the carbon chain increases in length, solubility in water decreases. All aldehydes and ketones are soluble in organic solvents and are generally less dense than water.
Phenols
Phenols have a hydroxyl group attached to an aromatic ring.
The parent compound is phenol.
Chemical formula:
Also known as monohydroxybenzene or carbolic acid.
Properties:
Colorless crystalline solid.
Melting point: .
Highly poisonous.
Causes chemical burns upon skin contact.
More acidic than alcohols and water.
Boiling point: nearly .
Moderately soluble in water.
Highly combustible.
Common phenols: catechol, resorcinol (m-dihydroxybenzene), and hydroquinone (para-dihydroxybenzene).
Uses:
Disinfectant and antiseptic.
Intermediate in making plastics, explosives, drugs, and dyes.
Antioxidants in foods.
Applications in herbicides and pesticides.
Specific phenols and uses:
Cresol:
Bactericides
Pesticides
Preservatives in some pharmaceuticals
Disinfectants.
Catechol: produce pesticides.
Salicylic acid: treat warts, dandruff, acne, fungal infections (ringworm), and ichthyosis.
Alphanaptol:
Production of dyes
Insecticides
Pharmaceuticals.
Tetrahydrocannabinol: principal active component of marijuana.
Phenolphthalein: indicator in acid-base titrations.
Chemical behavior:
The hydroxyl group activates the aromatic ring toward electrophilic substitution.
Especially at the ortho and para positions.
Undergoes halogenation and nitration more readily than benzene.
Due to its activation.
Summary: aromatic compounds with a hydroxyl group attached to an aromatic ring, with industrial, medicinal, and biological roles distinguished by acidity, hydrogen bonding, and reactivity on the aromatic ring.
Production: obtained from coal tar; several commercial methods are used to produce phenol synthetically.
Differential Tests for Phenol
Litmus test: Blue litmus paper turns red due to acidity.
Ferric chloride test: Aqueous solution of phenol reacts with freshly prepared ferric chloride, giving a colored complex.
Phenol and resorcinol produce violet or blue.
Catechol produces a green color.
Salicylic acid produces violet.
Alpha naphthol:
No specific coloration
With alcohol, it yields a violet-blue coloration.
Cresol produces a violet or blue color.
Bromine water test: Phenol undergoes electrophilic substitution reaction with bromine.
Addition of bromine water produces a brown color that disappears, forming a white precipitate of tribromophenol.
Aldehydes and Ketones
Acetone is the simplest and most common ketone.
Uses include nail polish remover, paints, varnish, and resins.
It is also produced during fat metabolism.
Aldehydes have the carbonyl group at the end of the carbon chain bonded to at least one hydrogen.
Ketones have the carbonyl group within the carbon chain bonded to two carbon atoms.
Key difference: Aldehydes are readily oxidized to carboxylic acid, while ketones resist oxidation under normal conditions.
Aldehydes are generally more reactive than ketones.
Due to less steric hindrance and electronic effects.
Aldehydes and Ketones:
Reactive organic chemical compounds.
The word aldehyde is a combination of alcohol and dehydrogenated.
Form carboxylic acids when they are further oxidized.
General formula of aldehyde is RCHO, where R is hydrogen or an alkyl or aryl group (bonded to one hydrogen).
Common names for aldehydes are often derived from the name of the acid that it will form.
Ketones consist of an alkyl chain and a double-bonded oxygen attached to one of the carbon atoms in the chain.
In ketones, oxygen is bonded to a secondary or middle-of-the-chain carbon.
Ketones are less chemically active than aldehydes and are used in perfumes and paints to stabilize other ingredients.
Other uses include adhesives, components of thinners, printing inks, cleaning agents, tanning, solvents, preservatives, hydraulic fluids, and as intermediates in the chemical industry.
Acetone, acetoacetate, and beta-hydroxybutyrate are ketones generated from carbohydrates, fatty acids, and amino acids in our bodies.
Ketones are elevated in blood after fasting (including a night of sleep) and during starvation since carbohydrates will be broken down.
Both aldehydes and ketones contain the carbonyl group (carbon-to-oxygen double bond).
Aldehydes have at least one hydrogen bonded to the carbonyl group.
Whereas ketones have one alkyl or aryl aromatic group bonded to the carbonyl group.
Common names for aliphatic aldehydes are derived from the common names of the carboxylic acids.
The "ic" or "oic acid" ending of the acid name is dropped and replaced with the suffix "aldehyde."
Formaldehyde (one-carbon aldehyde) is derived from formic acid (one-carbon acid).
Acetaldehyde (two-carbon aldehyde) is derived from acetic acid (two-carbon acid).
Aromatic aldehydes containing an aldehyde group bonded to an aromatic ring are named after the corresponding carboxylic acid.
Benzaldehyde is derived from benzoic acid.
Preparation of Aldehydes and Ketones
Prepared through oxidation of alcohols using an oxidizing agent like potassium dichromate.
Methanol reacts with oxygen in air in the presence of a silver or copper catalyst to form formaldehyde and water.
Methanol + O2 \xrightarrow[Ag \or Cu]{} Formaldehyde + H2O
Properties
Boiling Point: Aldehydes and ketones cannot hydrogen bond to themselves because no hydrogen atom is attached to the oxygen atom of the carbonyl group.
They have lower boiling points compared to alcohols.
Solubility: Aldehydes and ketones are about the same solubility as alcohols and ethers.
Formaldehyde, acetaldehyde, and acetone are soluble in water.
As the carbon chain increases in length, solubility in water decreases.
All aldehydes and ketones are soluble in organic solvents and are generally less dense than water.
Combustibility:
Aldehydes are either gas or volatile liquids.
Are highly flammable.
Flash points below .
Which is especially dangerous.
Ketones are reactive with many acids and bases.
Liberate heat and flammable gases.
Ketones react with reducing agents.
Produce a flammable gas and heat.
Chemical Properties
Aldehydes undergo both oxidation and reduction reactions; ketones undergo reduction reaction only.
Because of the double bonding of their functional group, both aldehydes and ketones can undergo addition reaction.
Aldehydes and ketones are easily reduced to alcohols:
Either by elemental hydrogen in the presence of a catalyst (hydrogen or nickel)
Or by chemical reducing agents such as lithium aluminum hydride or sodium borohydride.
Aldehydes will yield primary alcohols.
Whereas ketones yield secondary alcohols.
Aldehyde \xrightarrow[H_2 \or Ni]{} Primary \ Alcohol
Ketone \xrightarrow[H_2 \or Ni]{} Secondary \ Alcohol
Aldehydes are easily oxidized to carboxylic acids by a variety of oxidizing agents, including oxygen of the air.
Oxidation is the reaction in which aldehydes differ most from ketones.
Aldehydes are easily oxidized to carboxylic acid by potassium dichromate and by mild oxidizing agents such as silver and copper ions.
Tests
Tollens' Test: (Silver Mirror test) detects the presence of aldehyde-containing carbohydrates by oxidizing aldehydes using silver ions, resulting in the formation of metallic silver.
Positive test: Appearance of a silver mirror on the inner wall of the tube.
Fehling's and Benedict's Test: Uses copper ions in an alkaline medium to oxidize the aldehyde group to an acid, reducing the blue copper ions to brick-red copper oxide which precipitates during the reaction.
This test can be used as a general test for carbohydrates that have an available aldehyde group.
Schiff Test: A colorless solution indicates a negative result (aldehyde is absent).
If the solution turns magenta, the result is positive (aldehyde is present).
Brady's Test: Utilizes 2,4-dinitrophenylhydrazine to detect aldehydes and ketones.
Acetaldehyde: Immediate yellow precipitate.
Propanone: Yellow crystalline precipitate after one to two minutes.
Para-methoxybenzaldehyde: Immediate red precipitate.
Legal's Test: Acetoacetic acid and acetone will form violet colored complexes with sodium nitroprusside in an alkaline medium.
Ketone bodies (acetoacetic acid, acetone, and beta-hydroxybutyric acid) are produced by the liver, and ketones in the urine are caused by an abnormal carbohydrate metabolism.
Ketonuria is frequently a sign of diabetic ketosis, insulin overdose, starvation, dangerous metabolic abnormalities during pregnancy, and vomiting of infants.
Common Aldehydes and Ketones
Formaldehyde (Methanal): A poisonous, irritating gas that is highly soluble in water.
Marketed as a 37% aqueous solution called formalin, which also contains 10-15% methanol to keep formaldehyde from polymerizing.
Largest use is in the manufacture of polymers.
Formaldehyde readily polymerizes to form a linear solid polymer (paraformaldehyde) which releases formaldehyde when heated.
Formaldehyde has been used to preserve biological samples.
Ingestion of formaldehyde may cause abdominal pains which may lead to coma and death.
Henner's Test: Detects the presence of formalin using concentrated sulfuric acid in the presence of ferric chloride.
A violet to purple colored ring indicates the presence of formalin or formaldehyde.
Acetaldehyde: A volatile liquid with a pungent, irritating odor; has a general narcotic action and may cause respiratory paralysis.
Principal use is as an intermediate in the manufacture of other chemicals such as acetic acid.
Acetaldehyde is found in humans following ingestion of ethanol and is produced in the liver as the first step in detoxifying ethanol.
Acetaldehyde slows protein synthesis, increases oxidative damage to the liver, and hampers the liver's ability to export needed chemicals into the bloodstream.
Acetone and Methylethylketone (MEK): Ketones are widely used as organic solvents, and acetone in particular is used in very large quantities.
Acetone removes paints, varnishes, and finger nail polish, and as a solvent in the plastics industry.
MEK is also widely used as a solvent.
Acetone is formed in the human body as a byproduct of lipid metabolism.
Summary: Aldehydes and Ketones
Aldehydes: Carbonyl at chain end, easily oxidized, and more reactive.
Ketones: Carbonyl within chain resistant to oxidation and less reactive.
Both share nucleophilic addition chemistry centered on the polar carbonyl group.
Carboxylic Acids
Almost present in all food products, especially foods with a sour taste; esters are derivatives responsible for the sweet and pleasant odor and taste of foods.
Carboxylic acids are characterized by the presence of a carboxyl group (COOH), which consists of a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group attached to the same carbon.
An organic compound that has a carboxyl group is the carboxylic acid.
The carboxyl group is the functional group which contains the carbon-oxygen double bond and an -OH group, which is also attached to the same carbon atom.
The formula for carboxylic acid is RCOOH.
Carboxylic acid can be either aliphatic or aromatic.
Aliphatic Carboxylic Acids
Formic acid gets its name from the Latin word forbica meaning ant.
Acetic acid is found in vinegar and gets its name from the Latin word for vinegar.
Butyric acid comes from the Latin term for butter, since it is a constituent of butter fat.
The , and carbon acids are found in goat fat, and their names are derived from the Latin word for goat.
Stearic acid is seen in beef fat.
Acetic acid is the most common organic acid; pure acetic acid yields glacial acetic acid.
Physical Properties of Carboxylic Acids
Each aliphatic carboxylic acid molecule is polar and consists of a carboxyl group and a hydrocarbon group, which is represented by R.
The first four acids (formic through butyric) are completely soluble in water.
Beginning with pentanoic acid (valeric acid), water solubility falls sharply.
Acids with more than eight carbons are virtually insoluble in water.
The comparatively high boiling points are due to intermolecular attractions resulting from hydrogen bonding.
Carboxylic acids are generally weak acids that are only slightly ionized in water.
Example:
Chemical Properties of Carboxylic Acids
Carboxylic acids are used in acid-base titration and in substitution reactions for acid chlorides, acid anhydrides, esters, and amides.
Acid-Base Reaction: Acids have a sour taste, change blue litmus paper to red, form water solutions with values less than seven, and undergo neutralization reactions with bases to form water and salt.
Substitution Reactions: Can substitute acid chlorides, anhydrides, esters, and amides.
Acid Chloride Formation
Thionyl chloride reacts with carboxylic acid (elimination of water forms two molecules of carboxylic acid) to form the acid chloride.
Esters
A chemical compound derived from an acid in which at least one hydroxyl group is replaced by an alkyl group (substitution reaction of a carboxylic acid and an alcohol).
Esters are known for their distinctive odors and are commonly used for food aroma and fragrances.
The general formula of an ester is , where R is derived from carboxylic acid and R' from an alcohol.
Esters are formed by the reaction of an acid with an alcohol or phenol.
Esterification is one of the most important reactions of carboxylic acids.
Occurrence and Physical Properties
Natural and synthesized esters exist in almost endless variety.
Simple esters derived from monocarboxylic acids and monohydroxy alcohols are colorless, generally nonpolar liquids or solids.
Low polarity of ester molecules is substantiated by lower water solubility and boiling points than those of acids or alcohols.
Low and intermediate molar mass esters (up to in both acids and alcohols) are liquids with characteristic fragrant or fruity odors.
High molecular mass esters formed from acids and alcohols of 16 or more carbons are waxes.
Polyesters with very high molar masses, such as dacron, are widely used in the textile industries.
Chemical Properties
The most important reaction of esters is hydrolysis, the splitting of molecules through the addition of water. A catalyst is required.
In the laboratory, acid or base is employed as a catalyst for hydrolysis, and in living systems, enzymes act as catalysts.
Hydrolysis of esters involves reaction with water to form the carboxylic acid and an alcohol, catalyzed by strong acids (sulfuric acid, hydrochloric acid) or by certain enzymes.
Alkaline Hydrolysis (Saponification): Hydrolysis of an ester by making use of a strong base (sodium or potassium hydroxide) to produce alcohol and a salt (soap if the salt formed is from a high molar mass acid).
In saponification, the base is a reactant and not a catalyst.
Applications
Polyesters are formed using hydroxy acids (glycolic acid and lactic acid).
The hydroxyl group of one monomer reacts with the carboxylic acid of another monomer to form an ester, continuing polymer growth.
The finished polymer is a chain of esters (a polyester).
When the esters hydrolyze, the chain is broken, and the stitches dissolve.
The properties of the suturing material can be varied, allowing different thicknesses, elasticities, and dissolving rates.
Esters and Anhydrides of Phosphoric Acid
For phosphoric acid, the product of the esterification reaction is called a phosphate ester.
These esters have important biochemical functions.
The phosphate esters are used to tag many biochemicals, labeling them for specific biological uses.
For example, after a meal, blood sugar increases, and the liver absorbs the excess.
The sugar is immediately esterified, which ensures that it will be either metabolized or stored and will remain out of the bloodstream for the time being.
In living cells, phosphoric acid often connects different biochemicals by two ester bands.
Our cells' genetic material (DNA and RNA) is linked by phosphodiesters.
Nitrogen-Containing Compounds: Amines and Amides
Amines and amides are the two major classes of nitrogen-containing compounds.
Amines isolated from plants form a group of compounds called alkaloids.
Examples of common alkaloid compounds include quinine (used in the treatment of malaria).
Amides are nitrogen derivatives of carboxylic acid and are found as polymers commercially (nylon) and biologically (proteins).
Carboxylic acid reacts with ammonia to form the ammonia salts, and when heated, these ammonia salts lose a molecule of water and are converted to amide.
Physical Properties
Except for formamide (methanamide), which is a liquid, other unsubstituted amides are solids at room temperature; many are odorless and colorless.
Low molar mass amides are soluble in water, but solubility decreases quickly as molar mass increases.
The amide functional group is polar, and nitrogen is capable of hydrogen bonding.
The solubility of these molecules and their exceptionally high melting points and boiling points are the result of this polarity and hydrogen bonding between molecules.
Hydrolysis is one of the most important reactions of amides.
The amide will be cleaved into two parts: the carboxylic acid portion and the nitrogen-containing portion.
Requires the presence of a strong acid or a strong base (laboratory).
Amide hydrolysis occurs during the degradation of proteins by enzymatic reaction.
Protein digestion starts in the stomach, where proteins are made smaller, and some amino acids are released.
Because the stomach contains hydrochloric acid, the amino acids are liberated as carboxylic acids and amide salts.
Protein digestion is completed in the small intestine, and the amino acids are absorbed in the bloodstream.
Amines
Amines are capable of hydrogen bonding with water.
As a result, aliphatic amines with up to six carbons are quite soluble in water.
Methylamine and ethylamine are flammable gases with a strong ammoniacal odor.
Trimethylaminuria has a fishy odor, and high molar mass amines have obnoxious odors.
Preparation of Amines
Alkylation of ammonia: Substitution of alkyl groups for hydrogen atoms of ammonia by reacting ammonia with alkyl halides.
Successive reactions can form primary, secondary, and tertiary amines.
Reduction of amides and nitriles: Amides can be reduced with lithium aluminum hydride to give amines.
For example, acetanimide can be reduced to ethylamine.
When N and diethylacetamide is reduced, triethylamine is formed.
Reduction of aromatic nitro compounds: Aniline, the most widely used aromatic amine, is made by reducing nitrobenzene.
The nitro group can be reduced by several reagents like iron and hydrochloric acid, or tin and hydrochloric acid are commonly used.
Tests
Biuret Test: Chemical test to determine the presence of a peptide bond in a substance.
A colored coordination complex is formed between copper ions and carbonyl oxygen and an amide nitrogen of the peptide bond.
Once this complex has been formed, the solution turns from blue to purple.
The deeper the purple color is, the higher is the number of peptide copper complexes.
The intensity of the color is directly proportional to the number of peptide bonds present in the protein molecule that is reacting and also the number of protein molecules present in the reaction system.
Sodium hydroxide and potassium hydroxide provide the alkaline medium, and potassium sodium tartrate is added to chelate and thus stabilize the cupric ions in the solution or to maintain their solubility in alkaline solution.
Negative: remains blue in color (proteins are absent).
Positive: formation of purple color (proteins are present).
Ninhydrin Test: The amino group belonging to a free amino acid undergoes a chemical reaction with ninhydrin, which behaves as an oxidizing agent.
When exposed to ninhydrin, the amino acid undergoes oxidative deamination resulting in the liberation of carbon dioxide, ammonia, and an aldehyde along with hydron dantene.
The ammonia goes on to react with another ninhydrin molecule to form dichetohydrin, which is also known as the Ruhemann's complex.
This complex is responsible for the deep blue color, and when the analyte contains amino acids like proline a yellow colored complex is formed, and when asparagine is used, the color of the resulting complex is brown.
Interpretation:
Ammonia for primary or secondary amines: Deep purple color is obtained.
Hydroxyproline and proline will produce a yellow color.
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Chemical Properties
Aldehydes undergo both oxidation and reduction reactions; ketones undergo reduction reaction only.
Because of the double bonding of their functional group, both aldehydes and ketones can undergo addition reaction.
Aldehydes and ketones are easily reduced to alcohols either by elemental hydrogen in the presence of a catalyst (hydrogen or nickel) or by chemical reducing agents such as lithium aluminum hydride or sodium borohydride. Aldehydes will yield primary alcohols, whereas ketones yield secondary alcohols.
Aldehyde \xrightarrow[H_2 \or Ni]{} Primary \ Alcohol
Ketone \xrightarrow[H_2 \or Ni]{} Secondary \ Alcohol
Aldehydes are easily oxidized to carboxylic acids by a variety of oxidizing agents, including oxygen of the air. Oxidation is the reaction in which aldehydes differ most from ketones.
Aldehydes are easily oxidized to carboxylic acid by potassium dichromate and by mild oxidizing agents such as silver and copper ions.
Tests
Tollens' Test: (Silver Mirror test) detects the presence of aldehyde-containing carbohydrates by oxidizing aldehydes using silver ions, resulting in the formation of metallic silver.
Positive test: Appearance of a silver mirror on the inner wall of the tube.
Fehling's and Benedict's Test: Uses copper ions in an alkaline medium to oxidize the aldehyde group to an acid, reducing the blue copper ions to brick-red copper oxide which precipitates during the reaction. This test can be used as a general test for carbohydrates that have an available aldehyde group.
Schiff Test: A colorless solution indicates a negative result (aldehyde is absent). If the solution turns magenta, the result is positive (aldehyde is present).
Brady's Test: Utilizes 2,4-dinitrophenylhydrazine to detect aldehydes and ketones.
Acetaldehyde: Immediate yellow precipitate.
Propanone: Yellow crystalline precipitate after one to two minutes.
Para-methoxybenzaldehyde: Immediate red precipitate.
Legal's Test: Acetoacetic acid and acetone will form violet colored complexes with sodium nitroprusside in an alkaline medium. Ketone bodies (acetoacetic acid, acetone, and beta-hydroxybutyric acid) are produced by the liver, and ketones in the urine are caused by an abnormal carbohydrate metabolism.
Ketonuria is frequently a sign of diabetic ketosis, insulin overdose, starvation, dangerous metabolic abnormalities during pregnancy, and vomiting of infants.
Common Aldehydes and Ketones
Formaldehyde (Methanal): A poisonous, irritating gas that is highly soluble in water. Marketed as a 37% aqueous solution called formalin, which also contains 10-15% methanol to keep formaldehyde from polymerizing. Largest use is in the manufacture of polymers. Formaldehyde readily polymerizes to form a linear solid polymer (paraformaldehyde) which releases formaldehyde when heated. Formaldehyde has been used to preserve biological samples. Ingestion of formaldehyde may cause abdominal pains which may lead to coma and death.
Henner's Test: Detects the presence of formalin using concentrated sulfuric acid in the presence of ferric chloride. A violet to purple colored ring indicates the presence of formalin or formaldehyde.
Acetaldehyde: A volatile liquid with a pungent, irritating odor; has a general narcotic action and may cause respiratory paralysis. Principal use is as an intermediate in the manufacture of other chemicals such as acetic acid. Acetaldehyde is found in humans following ingestion of ethanol and is produced in the liver as the first step in detoxifying ethanol. Acetaldehyde slows protein synthesis, increases oxidative damage to the liver, and hampers the liver's ability to export needed chemicals into the bloodstream.
Acetone and Methylethylketone (MEK): Ketones are widely used as organic solvents, and acetone in particular is used in very large quantities. Acetone removes paints, varnishes, and finger nail polish, and as a solvent in the plastics industry. MEK is also widely used as a solvent. Acetone is formed in the human body as a byproduct of lipid metabolism.
Summary: Aldehydes and Ketones
Aldehydes: Carbonyl at chain end, easily oxidized, and more reactive.
Ketones: Carbonyl within chain resistant to oxidation and less reactive.
Both share nucleophilic addition chemistry centered on the polar carbonyl group.
Carboxylic Acids
Almost present in all food products, especially foods with a sour taste; esters are derivatives responsible for the sweet and pleasant odor and taste of foods.
Carboxylic acids are characterized by the presence of a carboxyl group (COOH), which consists of a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group attached to the same carbon.
An organic compound that has a carboxyl group is the carboxylic acid. The carboxyl group is the functional group which contains the carbon-oxygen double bond and an -OH group, which is also attached to the same carbon atom.
The formula for carboxylic acid is RCOOH.
Carboxylic acid can be either aliphatic or aromatic.
Aliphatic Carboxylic Acids
Formic acid gets its name from the Latin word forbica meaning ant.
Acetic acid is found in vinegar and gets its name from the Latin word for vinegar.
Butyric acid comes from the Latin term for butter, since it is a constituent of butter fat.
The , and carbon acids are found in goat fat, and their names are derived from the Latin word for goat.
Stearic acid is seen in beef fat.
Acetic acid is the most common organic acid; pure acetic acid yields glacial acetic acid.
Physical Properties of Carboxylic Acids
Each aliphatic carboxylic acid molecule is polar and consists of a carboxyl group and a hydrocarbon group, which is represented by R.
The first four acids (formic through butyric) are completely soluble in water. Beginning with pentanoic acid (valeric acid), water solubility falls sharply.
Acids with more than eight carbons are virtually insoluble in water.
The comparatively high boiling points are due to intermolecular attractions resulting from hydrogen bonding.
Carboxylic acids are generally weak acids that are only slightly ionized in water. Example:
Chemical Properties of Carboxylic Acids
Carboxylic acids are used in acid-base titration and in substitution reactions for acid chlorides, acid anhydrides, esters, and amides.
Acid-Base Reaction: Acids have a sour taste, change blue litmus paper to red, form water solutions with values less than seven, and undergo neutralization reactions with bases to form water and salt.
Substitution Reactions: Can substitute acid chlorides, anhydrides, esters, and amides.
Acid Chloride Formation
Thionyl chloride reacts with carboxylic acid (elimination of water forms two molecules of carboxylic acid) to form the acid chloride.
Esters
A chemical compound derived from an acid in which at least one hydroxyl group is replaced by an alkyl group (substitution reaction of a carboxylic acid and an alcohol).
Esters are known for their distinctive odors and are commonly used for food aroma and fragrances.
The general formula of an ester is , where R is derived from carboxylic acid and R' from an alcohol.
Esters are formed by the reaction of an acid with an alcohol or phenol.
Esterification is one of the most important reactions of carboxylic acids.
Occurrence and Physical Properties
Natural and synthesized esters exist in almost endless variety.
Simple esters derived from monocarboxylic acids and monohydroxy alcohols are colorless, generally nonpolar liquids or solids.
Low polarity of ester molecules is substantiated by lower water solubility and boiling points than those of acids or alcohols.
Low and intermediate molar mass esters (up to in both acids and alcohols) are liquids with characteristic fragrant or fruity odors.
High molecular mass esters formed from acids and alcohols of 16 or more carbons are waxes.
Polyesters with very high molar masses, such as dacron, are widely used in the textile industries.
Chemical Properties
The most important reaction of esters is hydrolysis, the splitting of molecules through the addition of water. A catalyst is required. In the laboratory, acid or base is employed as a catalyst for hydrolysis, and in living systems, enzymes act as catalysts.
Hydrolysis of esters involves reaction with water to form the carboxylic acid and an alcohol, catalyzed by strong acids (sulfuric acid, hydrochloric acid) or by certain enzymes.
Alkaline Hydrolysis (Saponification): Hydrolysis of an ester by making use of a strong base (sodium or potassium hydroxide) to produce alcohol and a salt (soap if the salt formed is from a high molar mass acid). In saponification, the base is a reactant and not a catalyst.
Applications
Polyesters are formed using hydroxy acids (glycolic acid and lactic acid).
The hydroxyl group of one monomer reacts with the carboxylic acid of another monomer to form an ester, continuing polymer growth.
The finished polymer is a chain of esters (a polyester).
When the esters hydrolyze, the chain is broken, and the stitches dissolve.
The properties of the suturing material can be varied, allowing different thicknesses, elasticities, and dissolving rates.
Esters and Anhydrides of Phosphoric Acid
For phosphoric acid, the product of the esterification reaction is called a phosphate ester. These esters have important biochemical functions. The phosphate esters are used to tag many biochemicals, labeling them for specific biological uses. For example, after a meal, blood sugar increases, and the liver absorbs the excess. The sugar is immediately esterified, which ensures that it will be either metabolized or stored and will remain out of the bloodstream for the time being.
In living cells, phosphoric acid often connects different biochemicals by two ester bands. Our cells' genetic material (DNA and RNA) is linked by phosphodiesters.
Nitrogen-Containing Compounds: Amines and Amides
Amines and amides are the two major classes of nitrogen-containing compounds.
Amines isolated from plants form a group of compounds called alkaloids. Examples of common alkaloid compounds include quinine (used in the treatment of malaria).
Amides are nitrogen derivatives of carboxylic acid and are found as polymers commercially (nylon) and biologically (proteins).
Carboxylic acid reacts with ammonia to form the ammonia salts, and when heated, these ammonia salts lose a molecule of water and are converted to amide.
Physical Properties
Except for formamide (methanamide), which is a liquid, other unsubstituted amides are solids at room temperature; many are odorless and colorless.
Low molar mass amides are soluble in water, but solubility decreases quickly as molar mass increases.
The amide functional group is polar, and nitrogen is capable of hydrogen bonding.
The solubility of these molecules and their exceptionally high melting points and boiling points are the result of this polarity and hydrogen bonding between molecules.
Hydrolysis is one of the most important reactions of amides.
The amide will be cleaved into two parts: the carboxylic acid portion and the nitrogen-containing portion.
Requires the presence of a strong acid or a strong base (laboratory).
Amide hydrolysis occurs during the degradation of proteins by enzymatic reaction.
Protein digestion starts in the stomach, where proteins are made smaller, and some amino acids are released.
Because the stomach contains hydrochloric acid, the amino acids are liberated as carboxylic acids and amide salts.
Protein digestion is completed in the small intestine, and the amino acids are absorbed in the bloodstream.
Amines
Amines are capable of hydrogen bonding with water. As a result, aliphatic amines with up to six carbons are quite soluble in water.
Methylamine and ethylamine are flammable gases with a strong ammoniacal odor.
Trimethylaminuria has a fishy odor, and high molar mass amines have obnoxious odors.
Preparation of Amines
Alkylation of ammonia: Substitution of alkyl groups for hydrogen atoms of ammonia by reacting ammonia with alkyl halides; successive reactions can form primary, secondary, and tertiary amines.
Reduction of amides and nitriles: Amides can be reduced with lithium aluminum hydride to give amines. For example, acetanimide can be reduced to ethylamine. When N and diethylacetamide is reduced, triethylamine is formed.
Reduction of aromatic nitro compounds: Aniline, the most widely used aromatic amine, is made by reducing nitrobenzene. The nitro group can be reduced by several reagents like iron and hydrochloric acid, or tin and hydrochloric acid are commonly used.
Tests
Biuret Test: Chemical test to determine the presence of a peptide bond in a substance. A colored coordination complex is formed between copper ions and carbonyl oxygen and an amide nitrogen of the peptide bond. Once this complex has been formed, the solution turns from blue to purple. The deeper the purple color is, the higher is the number of peptide copper complexes. The intensity of the color is directly proportional to the number of peptide bonds present in the protein molecule that is reacting and also the number of protein molecules present in the reaction system. Sodium hydroxide and potassium hydroxide provide the alkaline medium, and potassium sodium tartrate is added to chelate and thus stabilize the cupric ions in the solution or to maintain their solubility in alkaline solution.
Negative: remains blue in color (proteins are absent).
Positive: formation of purple color (proteins are present).
Ninhydrin Test: The amino group belonging to a free amino acid undergoes a chemical reaction with ninhydrin, which behaves as an oxidizing agent. When exposed to ninhydrin, the amino acid undergoes oxidative deamination resulting in the liberation of carbon dioxide, ammonia, and an aldehyde along with hydron dantene. The ammonia goes on to react with another ninhydrin molecule to form dichetohydrin, which is also known as the Ruhemann's complex. This complex is responsible for the deep blue color, and when the analyte contains amino acids like proline a yellow colored complex is formed, and when asparagine is used, the color of the resulting complex is brown.
Interpretation:
Ammonia for primary or secondary amines: Deep purple color is obtained.
Hydroxyproline and proline will produce a yellow color.
Asparagine will produce a brown color.
If no color change is observed, the analyte does not contain amino acids, amines, or ammonia.