Carboxylic acids

a. This question is about carboxylic acids. 

State the general formula of a carboxylic acid.

b. Name the carboxylic acid shown

a. The general formula of a carboxylic acid is C_nH_2n+1COOH

b. This is 3-methylbutanoic acid

Write a balanced symbol equation, including state symbols, for the reaction of propanoic acid with sodium hydrogen carbonate powder to form the soluble sodium propanoate salt and two other products.

A balanced symbol equation, including state symbols, for the reaction of propanoic acid with sodium hydrogen carbonate powder to form the soluble sodium propanoate salt and two other products

`CH_3CH_2COOH (aq) + NaHCO_3 (s) -> CH_3CH_2COONa (aq) + H_2O (l) + CO_2 (g)`

There is a conversion of propanoic acid into propan-1-ol and vice versa

a. Write an equation for propan-1-ol formation, using [H] to represent the reducing agent.

b.

i What type of reaction is propanic acid formation?

ii. Suggest a suitable reagent and conditions for this reaction

a. An equation for propan-1-ol formation

`CH_3CH_2COOH + 4[H] -> CH_3CH_2CH_2OH + H_2O`

The reduction of this alcohol will produce propan-1-ol and water under LiAlH₄

b.

i. This is an oxidation of primary alcohols or aldehydes

ii. A suitable reagent and conditions for this reaction include acidified K₂Cr₂O₇ or acidified KMnO₄ and refluxing.

Two students try to prepare 2‑hydroxybutanoic acid in the laboratory as shown figure below

Both students oxidise butane‑1,2‑diol to form P in reaction 1. One student then reduces P using LiAlH₄ . Q is formed. The other student reduces P using NaBH₄. R is formed.

A. State the reagents and conditions required for reaction 1.

B. Identify which of Q or R is 2‑hydroxybutanoic acid and explain the difference between reactions 2 and 3

A. A suitable reagent and conditions for this reaction include acidified K₂Cr₂O₇ or acidified KMnO₄ and refluxing. 

B. NaBH₄ cannot reduce carboxylic acid bcause it’s weaker reducing agent than LiAlH₄ which is only used for reducing carboxylic acid. Thus, R is 2‑hydroxybutanoic acid

A third student prepares 2‑hydroxybutanoic acid using propanal as the starting material as shown in the figure below. In step 1 the student reacts propanal with a mixture of NaCN and HCN.

A. Draw the mechanism for the reaction of propanal with the mixture of NaCN and HCN to form S.

B. Complete the equation for the reaction in step 2, when S is heated under reflux with HCl (aq).

A. The mechanism for the reaction of propanal with the mixture of NaCN and HCN to form S

B. The equation for the reaction in step 2, when S is heated under reflux with HCl (aq)

`C_2H_5CH(OH)CN + HCl + 2H_2O → C_2H_5CH(OH)COOH + NH_4Cl`

Two reaction sequences to produce glycolic acid are shown

A. Draw the structure of X

B. Name the reagent used for reaction 2

C. Name the mechanism for reaction 3

D. Suggest the essential condition for reaction 3

A. The structure of X is CH₂(OH)CN

B. The reagent used for reaction 2 is phosphoric acid or sulfuric acid

C. The mechanism for reaction 3 is free-radical substitution

D. The essential condition for reaction 3 is UV/light

Identify the types of reaction and the reagents for each step in the following synthesis of the ethyl ester X.

`CH_2=CH_2 → CH_3CH_2Br → CH_3CH_2OH → RCO_2CH_2CH_3 (X)`

Step 1: The conversion of an alkene into a bromoalkane by using HBr(g) as the reagent at room temperature via an electrophilic addition reaction

Step 2: The conversion from bromoalkane to alcohol by using the reagent NaOH(aq) + heat via a nucleophilic substitution reaction

Step 3: The conversion of an alcohol into an ester by heating with RCOOH and concentrated H₂SO₄ via an esterification reaction

Which reaction does not produce propanoic acid?

A. Heating propanenitrile under reflux with dilute sodium hydroxide

B. Heating propanenitrile under reflux with dilute sulfuric acid

C. Heating propanal under reflux with acidified sodium dichromate(VI)

D. Heating propanol under reflux with acidified sodium dichromate(VI)

The answer is A

Because it will create sodium propanoate and ammonia instead

B, C and D are incorrect because they will generate propanoic acid

Propionitrile, CH₃CH₂C ≡ N, is used to produce propanoic acid.

What are the conditions for this reaction?

A. NaOH

B. H⁺ / Na₂Cr₂O₇

C. NaBH₄

D. H⁺ / H₂O

The answer is D

A is incorrect because the nitriles will be hydrolyzed with OH^- under reflux, leading not to the production of carboxylic acid

B is incorrect because Na₂Cr₂O₇ will be used to oxdise propanol and propanal instead

C is incorrect because NaBH₄ is a weak reducing agent

Apples contain a compound called malic acid

Which substance will react with only one hydroxyl groups in malic acid under suitable conditions?

A. Na (s)

B. PCl₅

C. NaOH (aq)

D. `Cr_2O""_7^(2-)"/"H^+ (aq)`

The answer is D

 Carboxylic acid groups are not oxidised with acidified dichromate ions anymore. Therefore, alcohols could be oxidised without affecting carboxylic acid groups.

A is incorrect because sodium metals will react with three of these functional groups to create salt and hydrogen

B is incorrect because PCl will react with carboxylic acid groups to create acid chloride

`RCOOH + PCl_5 -> RCH_2Cl + POCl_3 + HCl`

C is incorrect because it is similar to sodium metals, thus, resulting in the production of salt and water