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Chapter 21: Q21-82E (page 726)

Epoxy adhesives are prepared in two steps. SN2 reaction of the disodium salt of bisphenol A with epichlorohydrin forms a “Pre-polymer,” which is then “Cured” by treatment with a triamine such as H2NCH2CH2NHCH2CH2NH2.

Draw structures to show how the addition of the triamine results in a strengthening of the polymer.

Short Answer

Expert verified

The Ring Opening occurs in the epichlorohydrin to overcome the strain present by the nucleophilic attack.Dehydration forms the polymer.The reactioninvolves the nucleophilic acyl substitution mechanism.

Step by step solution

01

Increases the tensile strength

Polymerization increases the tensile strength as it removes the ring Strains of the cyclopropyl ring and leads to a saturated product

02

Remove the Cyclic ring and increases the tensile strength

Therefore, Polymerization leading to the removal of cyclic ring strains increases the tensile strength of the polymer.

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Most popular questions from this chapter

21-36 When 4-dimethylaminopyridine (DMAP) is added in catalytic amountsto acetic anhydride and an alcohol, it significantly increases the rate of ester formation. The process begins with a reaction between acetic anhydride and DMAP to form a highly reactive acetylpyridinium intermediate that is more reactive than acetic anhydride itself. Propose a mechanism for this process that includes the formation and reaction of the acetylpyridinium intermediate.

21-72 Phenyl 4-aminosalicylate is a drug used in the treatment of tuberculosis. Propose a synthesis of this compound starting from 4-nitrosalicylic acid.

21-30 Electrostatic potential maps of a typical amide (acetamide) and an acyl azide (acetyl azide) are shown. Which of the two do you think is more reactive in nucleophilic acyl substitution reactions? Explain.

When an amide is formed from an acid chloride or an anhydride, two moles of base are required. However, when an ester is used as the starting material, only one equivalent of base is needed. Explain the reactivity in terms of basicity of the leaving groups.

21-70 Treatment of a carboxylic acid with trifluoroacetic anhydride leads to anunsymmetrical anhydride that rapidly reacts with alcohol to give an ester.
R−C∥O−OH→(CF3CO)2OR−C∥O−O−C∥O−CF3→R'OHR−C∥O−OR'+CF3CO2H
(a) Propose a mechanism for the formation of the unsymmetrical anhydride.
(b) Why is the unsymmetrical anhydride unusually reactive?
(c) Why does the unsymmetrical anhydride react as indicated ratherthan giving a trifluoroacetate ester plus carboxylic acid?
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