Question

Give formulas for compounds \(\mathrm{A}-\mathrm{G}\), and tell what is happening in each reaction. polystyrene \(+\mathrm{CH}_{3} \mathrm{OCH}_{2} \mathrm{Cl}(\mathrm{SnCl} 4) \rightarrow \mathrm{A}+\mathrm{CH}_{3} \mathrm{OH}\) \(\mathrm{A}+\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{OCONHCH}_{2} \mathrm{COO}^{-+} \mathrm{NHEt}_{3} \rightarrow \mathrm{B}+\mathrm{Et}_{3} \mathrm{NHCl}\) \(\mathrm{B}+\) dil. \(\mathrm{HBr} \rightarrow \mathrm{C}+\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{Br}+\mathrm{CO}_{2}\) \(\mathrm{C}+\) carbobenzoxyalanylchloride \(\rightarrow \mathrm{D}\) \(\mathrm{D}+\) dil \(\mathrm{HBr} \rightarrow \mathrm{E}+\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{Br}+\mathrm{CO}_{2}\) \(\mathrm{E}+\mathrm{HBr}\left(\mathrm{CF}_{3} \mathrm{COOH}\right)^{\rightarrow} \mathrm{F}\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{Br}\right)^{\rightarrow}+\mathrm{G}\)

Short answer

In this series of reactions involving polystyrene and various reagents, the following compounds are formed: A: Polystyrene-(CH2OCH3) B: Polystyrene-(CH2OCH3)-C6H5-CH2OC(O)NH-CH2-COO- C: Polystyrene-(CH2OCH3)-C6H5-CH2OC(O)NH-CH2-Br D: Polystyrene-(CH2OCH3)-C6H5-CH2OC(O)NH-CH2-C(O)-NH-Z (where Z denotes the carbobenzoxy protective group) E: Polystyrene-(CH2OCH3)-C6H5-CH2OC(O)NH-CH2-C(O)-NH-Z-Br F: Polystyrene-(CH2Br)-C6H5-CH2OC(O)NH-CH2-C(O)-NH-Z G: Polystyrene-C6H5-CH2OC(O)NH-CH2-C(O)-NH-Z-Br The reactions involve functionalization and alkylation of polystyrene, followed by a series of substitution reactions with various reactants.

Step-by-step solution

1. Reaction of polystyrene with CH3OCH2Cl (SnCl4)

In this first reaction, polystyrene reacts with CH3OCH2Cl in the presence of SnCl4 as a catalyst. The outcome of this reaction is the alkylation of polystyrene, resulting in the formation of compound A and methanol as a side product. A: Polystyrene-(CH2OCH3)

2. Reaction of compound A with C6H5CH2OCONHCH2COO- + NEt3

The second reaction involves compound A reacting with C6H5CH2OCONHCH2COO- in the presence of NEt3 (triethylamine). This reaction leads to the formation of compound B and the release of Et3NHCl. Compound B is expected to be a polystyrene derivative with a benzyl carbamate group. B: Polystyrene-(CH2OCH3)-C6H5-CH2OC(O)NH-CH2-COO-

3. Reaction of compound B with dil. HBr

In the third reaction, compound B undergoes reaction with dilute HBr. This reaction will result in the formation of compound C, bromobenzene, and carbon dioxide gas. The bromine atom from HBr will substitute the benzylic oxygen in compound B, forming Compound C. C: Polystyrene-(CH2OCH3)-C6H5-CH2OC(O)NH-CH2-Br

4. Reaction of Compound C with carbobenzoxyalanylchloride

In the fourth reaction, Compound C reacts with carbobenzoxyalanylchloride as a reagent, which allows the formation of compound D. This compound is a polystyrene derivative with a carbamate and a carbobenzoxyalanyl group. D: Polystyrene-(CH2OCH3)-C6H5-CH2OC(O)NH-CH2-C(O)-NH-Z (where Z denotes the carbobenzoxy protective group)

5. Reaction of Compound D with dil HBr

The fifth reaction involves the reaction of Compound D with dilute HBr. As a result of this reaction, compound E is formed along with the release of bromobenzene and carbon dioxide. The bromine atom from HBr substitutes the benzylic oxygen in compound D, forming compound E. E: Polystyrene-(CH2OCH3)-C6H5-CH2OC(O)NH-CH2-C(O)-NH-Z-Br

6. Reaction of Compound E with HBr (CF3COOH)

The final reaction involves compound E reacting with HBr in the presence of trifluoroacetic acid. This reaction results in a two-step transformation – first, the formation of compound F, followed by the formation of compound G. F: Polystyrene-(CH2Br)-C6H5-CH2OC(O)NH-CH2-C(O)-NH-Z G: Polystyrene-C6H5-CH2OC(O)NH-CH2-C(O)-NH-Z-Br In summary, the series of reactions involve the functionalization and alkylation of polystyrene, followed by a series of substitution reactions with various reactants, resulting in the formation of compounds A through G, with the molecular structure and transformations provided here.

Key concepts

Polystyrene Alkylation

Alkylation refers to the process where an alkyl group is transferred to a substrate. In the context of the provided exercise, polystyrene, a versatile and widely used polymer, undergoes alkylation. This step incorporates a methoxyethyl group from a reagent like CH3OCH2Cl onto the polystyrene chain, in the presence of a catalyst such as SnCl4.

The alkylation enhances polystyrene's reactivity by introducing a methoxyethyl group which can further react in subsequent steps. Such functionalization is crucial as it paves the way for further chemical modifications essential for creating specialized polymers with desired properties for various applications.

Benzyl Carbamate Group Formation

The formation of the benzyl carbamate group is a pivotal step in organic chemistry, especially relevant in the protection of amine groups during synthesis. This is illustrated in the exercise where compound A reacts with a benzyl carbamate reagent in the presence of triethylamine (NEt3).

The reaction leads to the introduction of a carbamate group into the polymer, creating a protected amine that can withstand further synthetic steps. This tactic is often employed in the synthesis of peptides and other complex molecules where precise control over reactive sites is crucial.

Bromobenzene Synthesis

Bromobenzene synthesis within this sequence showcases an important reaction involving the substitution of a hydrogen atom by a bromine atom on a benzene ring. As shown in the exercise, when compound B is treated with diluted hydrobromic acid (HBr), a bromobenzene derivative is generated alongside other products such as carbon dioxide.

This type of reaction demonstrates the versatility of halogenation, a common strategy in constructing more complex molecules, which serves as a foundational step for many other reactions in organic chemistry.

Carbamate Chemistry

Carbamate chemistry plays a significant role in organic synthesis, used for protection and as an intermediary in the production of other functional groups. The exercise illustrates this when the bromobenzene derivative reacts with carbobenzoxyalanylchloride, a reagent that contains both a carbamate and a protective carbobenzoxy group.

This step results in the compound being further functionalized, showcasing the importance of carbamate chemistry in creating complex organic molecules with specific properties and functions.

Carbobenzoxyalanyl Group Addition

Adding a carbobenzoxyalanyl group to a molecule serves as an intricate step in protecting amino acids during peptide synthesis. In the exercise, the addition of this group is part of the chemical transformation of the polymer's side chain, ensuring that the amino group is safeguarded throughout the reaction sequence.

This protection strategy is pivotal in synthesizing peptides and proteins as it allows for selective reactions to occur without interference from potentially reactive amino groups.

Chemical Functionalization of Polymers

The chemical functionalization of polymers, such as polystyrene, is showcased across the exercise as a series of steps that modify the polymer chain to introduce new functional groups. This process highlights the customizability of synthetic polymers, enabling the design of materials with specific characteristics suitable for targeted applications.

From alkylation to carbamate protection, every step demonstrates how polymers can be transformed to have distinct and desirable chemical properties through controlled, stepwise reactions.

Organic Synthesis Steps

The overall process of organic synthesis involves carefully orchestrated steps, each with a specific purpose, leading to the creation of complex molecules. In the exercise provided, we see a clear demonstration of how individual steps—from alkylation to the strategic addition of protective groups—can build up the structure of a complex polymer.

Effective organic synthesis requires a deep understanding of these steps and their sequence, a meticulous design of the synthetic strategy, and precise execution to ensure the desired outcome is achieved, always keeping in mind the compatibility and reactivity of functional groups at different stages.