(b) One of your illustrious colleagues continues his/her education and finally obtains employment with a renowned pharmaceutical company as an organic chemist. He or she is asked to synthesize pantothenic acid because the company wants to use it to prepare a synthetic form of coenenzyme A. Your colleague devises a seven-step synthesis for pantothenic acid:

(1) Isobutyraldehye + formaldehyde + NaOH/H2O → II (C5H10O2)
(2) II + NaCN → (C6H10O2 NNa) + H2O → III (C6H11O2 N) + NaOH
(3) III + H2O + H2SO4 + heat → IV (C6H12O4) + NH4HSO4
(4) IV + H3O+ + heat → V (C6H10O3)
(5) V + NaOH + heat → VI (C6H11O4Na)
(6) VI + sodium 2-aminopropionate → sodium pantothenoate + H2O
(7) Sodium pantothenoate + HCl(aq) → pantothenic acid + NaCl(aq)

(a) Suggest structures for II, III, IV, V, and VI.

(b) Give a brief rationale for the non-basic activity of the nitrogen in pantothenic acid.

(c) Write chemical equations to explain the reactions of pantothenic acid with NaOH, ethyl alcohol, and hot NaOH as described in (a), (b), and (c) above.

(a) To suggest structures for II, III, IV, V, and VI, we need to analyze each step of the synthesis and determine the molecular changes that occur.

Step 1:
Isobutyraldehyde + formaldehyde + NaOH/H2O → II (C5H10O2)

In this step, isobutyraldehyde and formaldehyde react in the presence of NaOH and water to form compound II (C5H10O2). Without more specific information, we cannot determine the exact structure of compound II.

Step 2:
II + NaCN → (C6H10O2 NNa) + H2O → III (C6H11O2 N) + NaOH

In this step, compound II reacts with NaCN to form a compound with a sodium salt. Upon neutralization, we obtain compound III (C6H11O2N). Without more specific information, we cannot determine the exact structure of compound III.

Step 3:
III + H2O + H2SO4 + heat → IV (C6H12O4) + NH4HSO4

In this step, compound III undergoes a hydrolysis reaction in the presence of water, H2SO4, and heat to form compound IV (C6H12O4) and NH4HSO4 as a byproduct.

Step 4:
IV + H3O+ + heat → V (C6H10O3)

In this step, compound IV reacts with H3O+ and heat to undergo a dehydration reaction, resulting in the formation of compound V (C6H10O3).

Step 5:
V + NaOH + heat → VI (C6H11O4Na)

In this step, compound V reacts with NaOH and heat to form compound VI (C6H11O4Na). The specific reaction conditions and structural information of compound V determine the exact structure of compound VI.

Step 6:
VI + sodium 2-aminopropionate → sodium pantothenoate + H2O

In this step, compound VI reacts with sodium 2-aminopropionate to form sodium pantothenoate and water as a byproduct. The structure of sodium pantothenoate depends on the structural information of compound VI and sodium 2-aminopropionate.

Step 7:
Sodium pantothenoate + HCl(aq) → pantothenic acid + NaCl(aq)

In this step, sodium pantothenoate reacts with hydrochloric acid (HCl) to form pantothenic acid and sodium chloride (NaCl) as a byproduct.

(b) The non-basic activity of the nitrogen in pantothenic acid can be rationalized by considering the functional groups present in the molecule. Pantothenic acid contains two carboxylic acid groups (-COOH) and an amine group (-NH2). The carboxylic acid groups are acidic due to the donation of a proton (H+) from the -COOH group. On the other hand, the nitrogen in the amine group tends to act as a base, accepting a proton (H+) to form a positively charged ammonium ion (NH3+).

The non-basic activity of the nitrogen in pantothenic acid is likely due to the presence of the neighboring carboxylic acid groups, which are more acidic and can attract the proton instead of the nitrogen. The nitrogen lone pair is involved in resonance with the adjacent carbonyl group, which stabilizes the structure of pantothenic acid and reduces the basicity of the nitrogen.

(c) Chemical equations for the reactions of pantothenic acid with NaOH, ethyl alcohol, and hot NaOH:

Reaction with NaOH:
Pantothenic acid + NaOH → Sodium pantothenate + H2O

Reaction with ethyl alcohol:
Pantothenic acid + Ethyl alcohol → Ethyl pantothenate + H2O

Reaction with hot NaOH:
Pantothenic acid + NaOH (hot) → Sodium pantothenate + H2O

(a) Structures for II, III, IV, V, and VI:

II: C5H10O2
III: C6H11O2N
IV: C6H12O4
V: C6H10O3
VI: C6H11O4Na