Carboxylic Acids

Question 1

Aliphatic carb acid boiling point:-

Answer 1

Higher than alcohols b/c the OH bond is even more polar than in an alcohol bc of the adjacent c=o group and they have a molecular structure which enables them to form more H bonds than simple alcohols.

Question 2

Carb acid solubility:-

Answer 2

Smaller molecules e.g methanoic and ethanoic are completely miscible w/ H2O (dissolve) bc they can form H bonds w/ H2O molecules. Bigger hydrocarbon chain = less soluble because only the OH group can form the H bonds- can be outweighed if rest of molecule is relatively large and non-polar.

Question 3

Carboxylic acid from primary alco/aldehyde oxidation:-

Answer 3

Acidified Potassium dichromate as oxidising agent, heat under reflux.
E.g CH3CH2OH + 2[O] -> CH3COOH + H2O

Question 4

Carboxylic acid-base reactions:-

Answer 4

Reacts same way as inorg acids. Weak acids so slower. When writing salt formula, put metal/ammonium ion next to -COO^- group e.g (CH3COO^-)2 Mg^2+. Get rid of acid’s last hydrogen as gas.

Question 5

Ester melting/boiling point:-

Answer 5

Lower than their isomeric carboxylic acids bc the acids form lots of H bonds, esters don’t (they only form weaker induced and permanent dp-dp forces = less energy to break.)

Question 6

Ester solubility:-

Answer 6

Less soluble because carb acids can form H bonds to water much better.

Question 7

Sequence in ester structural formulae:-

Answer 7

-COOC-

Question 8

Naming esters:-

Answer 8

Use carboxylic acid part as root for name alongside other part used e.g Butanoic acid + Phenol = phenyl butanoate.

Question 9

Esterification w/ an alcohol general reaction:-

Answer 9

Carb acid + alco -> ester + H2O

Question 10

Ester from carb acid and alcohol visualisation:-

Answer 10

Alcohol’s carbon chain replaces H from carb acid’s OH group (have O between the parts of the two reactants).

Question 11

Esterification reaction type:-

Answer 11

Condensation reaction- 2 molecules joined to make a larger product but a small molecule i.e H2O is eliminated in the process.

Question 12

Carb acid + alco conditions:-

Answer 12

Heat w/ conc H2SO4 catalyst. Better with reflux

Question 13

Alco + carb acid reversibility:-

Answer 13

Reversible equilibrium so yields can be low

Question 14

Carb acid + alco rate:-

Answer 14

Slow reaction

Question 15

Carb acid + phenol for esters:-

Answer 15

Carb acid can’t be used with phenols as it’s too slow.

Question 16

Acid anhydride:-

Answer 16

Formed by carb acid dehydration. Think of as 2 identical carb acids joined at OH w/ H2 given off

Question 17

Structural formulae in anhydride:-

Answer 17

Look for COOCO

Question 18

Anhydride + alco esterification:-

Answer 18

Non COOCO parts are bonded to C in ester and C in carboxylic acid, non OH part of alcohol bonds to O in ester.

Question 19

Ester functional group:-

Answer 19

C with single bonded O, double bonded O and an R group. Different group bonded to single bonded O.

Question 20

Acid anhydride + alco general equation:-

Answer 20

Anhydride + alcohol -> ester + carb acid

Question 21

Alco + anhydride conds:-

Answer 21

Gentle heat, no catalyst needed.

Question 22

Advs of anhyd + alco esterification due to anhyd’s higher reactivity:- (2)

Answer 22

• Milder conds- need for strong acid catalyst for carb acid might cause further reactions of other functional groups in the molecule.
• the reaction of acid anhydrides w/ alcohols is irreversible but that of carboxylic acids is reversible = higher yield w/ anhydrides.

Question 23

Ester usage:-

Answer 23

Low Mr esters are volatile and have fruity smells, used in flavourings and perfumes.

Question 24

Base catalysed ester hydrolysis:-

Answer 24

Products = alcohol + salt of carboxylic acid, not acid itself.
E.g methyl propanoate (C4H8O2) + HO^-> C3H5O2^- + H3C-OH

Question 25

Base catalysed hydrolysis conds:-

Answer 25

Reflux w/ aqueous NaOH

Question 26

Converting salt from base catalysed to parent carboxylic acid:-

Answer 26

Neutralise w/ aqueous acid to convert salt into carboxylic acud and distil off the carboxylic acid.

Question 27

Base catalysed yield:-

Answer 27

Irreversible so high yield.

Question 28

Acid catalysed hydrolysis:-

Answer 28

Ester + H2O -> carb acid + alcohol.
Reflux w/ aqueous HCl.
Lower yield as reversible (reverse of esterification) so doesn’t go to completion.

Question 29

Acyl chlorides;-

Answer 29

Carboxylic acid derivative where -OH group is replaced by -Cl. RCOCl.

Question 30

Naming acyl chlorides:-

Answer 30

Changing -oic ending for parent carboxylic acid to
-oyl chloride.
E.g CH3COCl = ethanoyl chloride.

Question 31

Preparation of acyl chlorides:-

Answer 31

RCOOH + SOCl2 (thionyl chloride) -> RCOCl + SO2 + HCl.

Question 32

Acyl chloride reactivity:-

Answer 32

V. reactive- chloride readily leave as Cl^- so that it can be replaced by other groups.

Question 33

E.g of friedel-crafts acylation equation:-

Answer 33

Benzene + CH3COCl ->

Benzene ring w/ COCH3 branch + HCl.

Question 34

Carboxylic acid from acyl chloride:-

Answer 34

RCOCl + H2O -> RCOOH + HCl

Question 35

Ester from acyl chloride + alcohol:-

Answer 35

Product = ester + HCl, joing where OH is on alcohol.

Question 36

Advs of acyl chloride esterification vs carb acid esterification:-

Answer 36

No heating needed, high yield and can be used to esterify phenols which won’t directly react w/ carboxylic acids.

Question 37

Another way oxidising ethanol to carboxylic acid:-

Answer 37

Oxygen from the air in the presence of suitable bacteria, used to manufacture vinegar.