Chapter 20: Carboxylic Acids

Carboxylic Acid

R-COOH

Aliphatic Acids: Alkyl group (c chain) bonded to the COOH

• seen with fatty acids

Aromatic Acids: have aryl group (ex benzenen) attached to the cooh

Aliphatc Acids

Carboxylic acid group that has a long chain carbon (alkyl group) attached to the COOH

Carboxylic acid IUPAC

Alkane or Alkene —> Alkoic aicd

• the cooh’s carbon becomes the 1st numbered C

Cylclic Acids

Aryl ring attached to a COOH group

Cycloalkanes + COOH —> cycloalkanecarboxylic acids

Aromatic Acids + COOH —> benzoic acid

Benxoid compounds + 2 COOH —> phthalic acid

Dicarboxylic Acids

Aliphatic acids (acids with long carbon chain) + 2 COOh groups on its ends = Dicarboxylic Acid

• IUPAC numbering started from the coxy group closests to the long carbon chains substituent

Carboxyl Structure + Resonance forms

• bond angles are 120 with SP2 carbon hybridized (SP2 = carbon bonded to 3 groups)

Carboxy Boiling Pt

Higher than OH (h-bonds similar)

• able to do dimer formation —> high bp

Carboxyl Groups BP order

Phthalic (dicarboxy) > Aromatic COOh > Long chain aliphatic COOh > short chain COOH

Carboxylic Acids Melting Points

Aliphatic Carboxylic Acids

• Shorter carbon chain —> Low melting Point

• Longer carbon cahin —> melting point increases

• Longer carbon alkyl chains —> pack togeter strong IMFs —> higher melting poimt —> SOLDIFIES AFTER C8

Longer c chain = stronger packing = strong imfs = high MP (solid at c8)

Carboxylic Acids Melting Point Regarding = bonds

More cis double bonds = more bending = less tightly packed = lower melting point

• lower melting pt = lower temp needed for the carboxylic acid to turn from solid to liquid

Carboxylic Acids Solubility

Longer carbon chaines subsistuted COOH = Lower water solubility

• longer chains = less soluble in water (BUT MORE SOLUBLE IN OH)

• shorter chains = more soluble in water = less soluble in OH

All carboxylic acids able to dissolve (are soluble) in nonpolar solvents —> dissolves as a dimer

• nonpolar solvents = ex chlorofom

Carboxylic Acid Acidity

The longer the carbon R chain is = less acid

• LC c chain = less acidic, shrot c chain = more acidic

  • Less acidic = high pka value, low ka

  • more acidic = low pka, high ka

• RCOOH + h2o = RCOO- + h30+

RCOOH is more acidic than OH

• this is due to RCOOH allowing for resonance stablaizaiton with the c’s neg charge being shared with the O’s

Carboxylic acid substituent effect on acidity

The closer the COOH is to the substituent of the carbon chain = acidity increases

• substituent groups pull the RCOOH’s electrons away = making it more acidic (with stronger effect seen when in closer proximity)

Acid Salts IUPAC

start by naming the cation

• the acid name = acetate

  • id —> ate

Carboxylic Acid Salts

Carboxylic —> NaOh —> Converts to Slat

Salt —> HCl —> REconverts back to carboxylic acid

Properties of the Acid Salts

The salts are solids (high MP) with no order

• soluble in water slats contain Na, K, Li and NH4

• Insoluble in waters contain metal ions: Ca

Acid salts are solids with high mp (& no order)

• salts w/ Na, K, Li, and NH4 are soluble in water

• Metalic ion salts are insoluble in water (ie. Ca)

Acid Purification

Same thing as creating acid salt and converting back to carbozyilic acid

RCOH —> NaOH —> RCOO- —> HCL —> RCOOH

Some important acds

Acetic acid : Ch3COOH

Fatty acids: just long carcbon chained COOHs

Benzoic Ring: Benzne + Oh (formed from toule + KMnO4/H2O/Heat)

Adipic Acid: A dicarbozylic acid (cooh on its ends of the carbon chain)

Carboxylic Acid Synthesis

1. Primary alcohol oxidation to carboxylic acid

   1. uses H2CO7 (chromic acid) + TEMPO + NaOCl

2. alkene oxidation to carboxylic acid

   1. uses KMnO4

3. alkyl benzene oxidation to benzoic acid

   1. uses Na2Cr2)7 + H2SO4 or KMnO4 + H20

Grignard Synthesis

Grignard Reagent: Mg-X

• Benze + x —> Mg + ether —> CO2 —> Carboxylate Salt

• Carboxylate salt can change O- to OH through H20 or H+ protonation

• GRIGNARD REAGENT + CO2 + H —> CARBOXYLIC ACID

Hydrolysis of Nitriles

NITRILE: C≡N

R-Ch2-x (primary alkyl group) + CN (nitirle) —> R-Ch2-C≡N (nitrile) —> H+, H20, or -OH, H20 —> carboxylic acid

Acid Derivatives

The group attached to the acyl cabron (RCO) determines what tupe of acid derivative it is

• can have substitution of Oh, X. OR, or NH2

• NUC ATTACH SUBSTITUTENT ALLOWS FOR THE INTERCONVERSIONS OF THESE DERIVATIES (

  • acid chloride is most easily interconverted

derivative

cl: acid chloride

OR: ester

NH2: amine

OH: carboxylic acid

Fischer Esterfication

Carboxylic acid + R-OH + H —> produces ester

Carboxylic acid + (R-OH)2 + H —> ester hydrate —> H + ROH—> ester

Acid Chloride

• good leaving group for nuc attack

• synthesized by carboxylic acid + socl2 —> acid chloride

Acid Chloride to ester

Carboxylic acid —> socl2 —> acid chloride —> R-OH + Cl —> ester

Acid chloride to amide

Acid Chloride + R-NH2 —> cl replaced by NH2-R —> amide

Amide —> NaOH → simpler amide (1 amide becomes 2 amide)

Reuction to primary alcohol

acid + LiAlh/H3O+ —> R-Ch2-Oh

for carboxylic acids

• carboxylic acid —> BH3/THF/ H30 —> r-Ch2-Oh

Reduction to form Aldehyde

Redction means using reducing agent

• reducing agent in this is LiAlH(O-t-bu)3

• acid chlorde + LiAlH(o-t-bu)3 —> aldehyde

Alkylation to form ketones

Carboxylic acid + Socl2 —> Acid chloride

Acid chloride + 2R-LI + RLI + H3O —> KETONE

• USES ORGNAOLITHIUM REAGENTS