12.1: Alcohols, Phenols, Thiols, and Ethers

Alcohol (C₂H₆O)

• The functional group known as a hydroxyl group replaces a hydrogen atom in a hydrocarbon.

• In the IUPAC system, alcohol is named by replacing the e of the corresponding alkane name with –ol. The common name of simple alcohol uses the name of the alkyl group followed by alcohol.

• Methanol (CH3OH): The simplest alcohol and is found in many solvents and paint removers.

• Ethanol (C2H5OH): It has been known as an intoxicating product formed by the fermentation of grains, sugars, and starches.

• Glycerol (C3H8O3): A trihydroxy alcohol and a viscous liquid obtained from oils and fats during the production of soaps.

• Ethylene Glycol (C₂H₆O₂): It is used as an antifreeze in heating and cooling systems. It is also a solvent for paints, inks, and plastics, and it is used in the production of synthetic fibers.

• Bisphenol A (C15H16O2): It is used to make polycarbonate, a clear plastic that is used to manufacture beverage bottles, including baby bottles.

• Thiols (R-SH): These contain a sulfur atom, shown in yellow-green in the ball-and-stick model, which makes a thiol similar to alcohol except that —OH is replaced by an —SH group.

Phenol (C6H6O)

• The hydroxyl group replaces a hydrogen atom attached to a benzene ring.

• These are found in several of the essential oils of plants, which produce the odor or flavor of the plant.

• The term phenol is the IUPAC name for a benzene ring bonded to a hydroxyl group, which is used in the name of the family of organic compounds derived from phenol.

• Eugenol (C10H12O2): It is found in cloves, vanillins, isoeugenol, and thymol.

• Thymol (C10H14O): It has a pleasant, minty taste and is used in mouthwashes and by dentists to disinfect a cavity before adding a filling compound.

Ether (C2H5)2O

• The functional group consists of an oxygen atom, which is attached to two carbon atoms.

• They have a bent structure like water and alcohols except both hydrogen atoms are replaced by carbon groups.

• The name of each alkyl or aromatic group attached to the oxygen atom is written in alphabetical order, followed by the word ether.

  • Example: Methyl Propyl Ether

• Ethers have been associated with anesthesia because diethyl ether was the most widely used anesthetic for more than a hundred years.

12.2: Properties of Alcohols

• Primary (1°) Alcohol: It has one alkyl group attached to the carbon atom bonded to the –OH group.

• Secondary (2°) Alcohol: It has two alkyl groups attached to the carbon atom bonded to the –OH group.

• Tertiary (3°) Alcohol: It has three alkyl groups attached to the carbon atom bonded to the –OH group.

Solubility of Alcohols in Water

• Alcohols with one to three carbon atoms are miscible in water, which means any amount of the alcohol is completely soluble in water.

• Alcohols with four carbon atoms are slightly soluble in water, and alcohols with five or more carbon atoms are insoluble.

Solubility of Phenols

• Phenol is slightly soluble in water because the —OH group can form hydrogen bonds with water molecules.

• Phenol is very corrosive and highly irritating to the skin; it can cause severe burns, and ingestion can be fatal.

• Joseph Lister: He is considered a pioneer in antiseptic surgery and was the first to sterilize surgical instruments and dressings with phenol, which was initially named carbolic acid.

  • Antiseptic: A substance applied to the skin to kill microorganisms that cause infection.

12.3: Aldehydes and Ketones

Aldehyde (C2H4O)

• The carbon of the carbonyl group is bonded to at least one hydrogen atom.

• That carbon may also be bonded to another hydrogen atom, a carbon of an alkyl group, or an aromatic ring.

• The aldehyde group may be written as separate atoms or as —CHO, with the double bond understood.

• In the IUPAC system, an aldehyde is named by replacing the e of the corresponding alkane name with –al.

  • Example: Ethanal; Propanal; Butanal.

• The aldehydes with carbon chains of one to four carbons are often referred to by their common names, which end in aldehyde.

  • Example: Formaldehyde; Acetaldehyde; Propionaldehyde

Ketones (CnH2nO)

• The carbonyl group is bonded to two alkyl groups or aromatic rings.

• The keto group (C = O) can sometimes be written as CO.

• In the IUPAC system, the name of a ketone is obtained by replacing the e in the corresponding alkane name with –one.

  • Example: Propanone; Butanone; 3-Pentanone

• In the common names, the alkyl groups bonded to the carbonyl group are named as substituents and are listed alphabetically, followed by ketone.

  • Example: Dimethyl ketone; ethyl methyl ketone

12.4: Reactions of Alcohols, Thiols, Aldehydes, and Ketones

• In a dehydration reaction, alcohols lose a water molecule when they are heated with an acid catalyst such as H2SO4.

  • The components H— and —OH are removed from adjacent carbon atoms of the same alcohol to produce a water molecule.

• Oxidation of Alcohols: In organic chemistry, it involves the addition of oxygen or a loss of hydrogen atoms. There is an increase in the number of carbon–oxygen bonds.

  • The oxidation of primary alcohol produces an aldehyde.

  • The oxidation of secondary alcohol produces ketones.

  • Tertiary alcohols do not oxidize readily because there is no hydrogen atom on the carbon bonded to the —OH group.

• Reduction of Alcohols: In organic chemistry, the product has fewer bonds between carbon and oxygen.

• Thiols also undergo oxidation by the loss of hydrogen atoms from each of the two —SH groups. The oxidized product contains a disulfide bond.

• Aldehydes oxidize further by the addition of another O to form a carboxylic acid, which has a carboxyl functional group.

• Aldehydes and ketones are reduced by sodium borohydride or hydrogen.

  • Aldehydes reduce to primary alcohols, and ketones reduce to secondary alcohols.

  • A catalyst such as nickel, platinum, or palladium is needed for the addition of hydrogen to the carbonyl group.

• Tollens’ Test: It uses a solution of Ag+ and ammonia, which oxidizes aldehydes but not ketones.

  • The silver ion is reduced and forms a “silver mirror” on the inside of the container.

    

• Benedict’s Test: It gives a positive result with compounds that have an aldehyde functional group and an adjacent hydroxyl group.

  

  • Because many sugars, such as glucose, contain this type of aldehyde grouping, Benedict’s reagent can be used to determine the presence of glucose in blood or urine.