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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

Bacteria typically develop a resistance to penicillins and other β-lactam antibiotics (see Something Extra in this chapter) due to bacterial synthesis of β -lactamase enzymes. Tazobactam, however, is able to inhibit the activity of the β -lactamase by trapping it, thereby preventing a resistance from developing.

(a) The first step in trapping is the reaction of a hydroxyl group on the β -lactamase to open the β -lactam ring of tazobactam. Show the mechanism.
(b) The second step is opening the sulfur-containing ring in tazobactam to give an acyclic imine intermediate. Show the mechanism.
(c) Cyclization of the imine intermediate gives the trapped β-lactamase product. Show the mechanism.

The step-growth polymer nylon 6 is prepared from caprolactam. The reaction involves the initial reaction of caprolactam with water to give an intermediate open-chain amino acid, followed by heating to form the polymer. Propose a mechanism for both steps, and show the structures of nylon 6.

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?

Assign structures to compounds with the following 1H NMR spectra:

(a)C5H10O2

IR:1735cm-1

(b)C11H12O2

IR:1710cm-1

21-69 We said in Section 21-6 that mechanistic studies on ester hydrolysishave been carried out using ethyl propanoate labeled with in theether-like oxygen. AssumethatO18− labeled acetic acid is your onlysource of isotopic oxygen, and then propose a synthesis of the labeledethyl propanoate.
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