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Chapter 27: Problem 658

The alkaloid hygrine is found in the coca plant. Suggest a structure for it on the basis of the following evidence: Hygrine \(\left(\mathrm{C}_{8} \mathrm{H}_{1}{ }_{5} \mathrm{ON}\right)\) is insoluble in aqueous \(\mathrm{NaOH}\) but soluble in aqueous HC1. It does not react with benzenesulfonyl chloride. It reacts with phenylhydrazine to yield a phenylhydrazone. It reacts with NaOI to yield a yellow precipitate and a carboxylic acid \(\left(\mathrm{C}_{7} \mathrm{H}_{13} \mathrm{O}_{2} \mathrm{~N}\right)\). Vigorous oxidation by \(\mathrm{CrO}_{3}\) converts hygrine into hygrimic acid \(\left(\mathrm{C}_{6} \mathrm{H}_{11} \mathrm{O}_{2} \mathrm{~N}\right)\)

Short Answer

Expert verified
In summary, the most likely structure for hygrine (\(\mathrm{C}_{8} \mathrm{H}_{15} \mathrm{ON}\)) contains a carbonyl group (either an aldehyde or a ketone) and an alkyl halide group attached to a tertiary carbon atom, considering its reactions with various reagents and its solubility in aqueous HCl. The structure can be represented as: \[ \begin{array}{c} \mathrm{C=O} \\ \mathrm{R_{1}} \mathrm{C}^{\ast}\mathrm{R}_{2}\mathrm{R}_{3} \mathbf{-} \mathrm{X} \\ \end{array} \] where R1, R2, and R3 are alkyl groups, and X is a halogen atom.

Step by step solution

01

Solubility in aqueous HCl and insolubility in aqueous NaOH

The first evidence suggests that hygrine contains acidic functional groups, because it is soluble in aqueous HCl (acidic solution) but not in a basic solution (aqueous NaOH). Based on this, the most common acidic functional groups in organic chemistry are the carboxylic acid (-COOH) and phenol (-OH) groups. However, phenols typically react with NaOH to form soluble salts, which is not the case for hygrine. Thus, we can rule out the phenol group. In addition, since hygrine reacts with phenylhydrazine to form a phenylhydrazone (see evidence #3), it must contain a carbonyl group (C=O).
02

Reaction with benzenesulfonyl chloride

The fact that hygrine does not react with benzenesulfonyl chloride indicates that it does not have a primary or secondary amine group (NH2 or NHR, where R is an alkyl group) since these groups react with benzenesulfonyl chloride.
03

Reaction with phenylhydrazine

As mentioned in step 1, the reaction of hygrine with phenylhydrazine to form a phenylhydrazone suggests the presence of a carbonyl group (C=O). This group can be found in aldehydes and ketones.
04

Reaction with NaOI

Reaction with NaOI yields a carboxylic acid with the empirical formula \(\mathrm{C}_{7} \mathrm{H}_{13} \mathrm{O}_{2} \mathrm{~N}\). We can deduce that hygrine loses one carbon atom during the reaction, suggesting the presence of an alkyl halide group (R-X, where R is an alkyl group, and X is a halogen atom) that can be substituted in a nucleophilic substitution reaction (SN2) with NaOI. Since there is no indication that a reduced or decarboxylated product is formed, this suggests that the IO- ion does not attack a carbonyl group.
05

Oxidation by CrO3

Vigorous oxidation by \(\mathrm{CrO}_{3}\) converts hygrine into hygrimic acid \(\left(\mathrm{C}_{6} \mathrm{H}_{11} \mathrm{O}_{2} \mathrm{~N}\right)\). This result implies that hygrine loses two carbon atoms during the oxidation process, suggesting the presence of an adjacent tertiary carbon atom and alkyl halide group (alkyl halides can be easily oxidized).
06

Suggesting a structure for hygrine

Considering all the given information, the structure of hygrine must contain a carbonyl group (either an aldehyde or a ketone) along with an alkyl halide attached to a tertiary carbon atom. The most likely structure for hygrine is: \[ \begin{array}{c} \mathrm{C=O} \\ \mathrm{R_{1}} \mathrm{C}^{\ast}\mathrm{R}_{2}\mathrm{R}_{3} \mathbf{-} \mathrm{X} \\ \end{array} \] where R1, R2, and R3 are alkyl groups, and X is a halogen atom.

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Most popular questions from this chapter

Many of the beautiful colors of butterflies' wings, autumn leaves, and flowers are due to the presence of flavone derivatives called anthocyanins. When anthocyanins are hydrolyzed in hydrochloric acid (to remove sugar residues), they produce aromatic oxygen-containing salts. One of these is delphinidin chloride. Explain why delphinidin chloride is aromatic. What is the hybridization of the heterocyclic oxygen in this compound?

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