The synthesis of epoxy resins is a multi-billion dollar industry worldwide. Epoxy resins are high pe — Organic Chemistry Chemistry Question
Epoxy resins
The synthesis of epoxy resins is a multi-billion dollar industry worldwide. Epoxy resins are high performance adhesives synthesised from the reaction of a bis-epoxide with a diamine. The bis-epoxide is made from H and epichlorohydrin, C. Compounds C and H can be synthesised according to the schemes below.
The synthesis of epichlorohydrin C begins with the reaction of propene with chlorine in the presence of light.
5.1 Draw the structures of A and B.
5.2 Give the formula of a suitable reagent for the conversion of B into epichlorohydrin C.
Model Answer
NaOH, or the formula of another suitable base.
The synthesis of H commences with the reaction of benzene with propene in the presence of an acid catalyst which gives D as the major product and E and F as minor products.
5.3 Draw the structures of D, E, and F from the following data:
D: Elemental composition: C 89.94 %, H 10.06 %; 6 signals in the 13C NMR spectrum.
E: Elemental composition: C 88.82 %, H 11.18 %; 4 signals in the 13C NMR spectrum.
F: Elemental composition: C 88.82 %, H 11.18 %; 5 signals in the 13C NMR spectrum.
Bubbling oxygen through a hot solution of D gives G which on exposure to acid gives phenol (hydroxybenzene) and acetone (propanone). G turns starch iodide paper from white to dark blue. G has 6 signals in the 13C NMR spectrum and the following signals in the 1H NMR spectrum: δ 7.78 (1H, s), 7.45 – 7.22 (5H, m), 1.56 (6H, s); addition of D2O results in the disappearance of the signal at δ = 7.78.
5.4 Draw the structure of G.
Exposure of phenol and acetone to hydrochloric acid gives compound H. The 13C NMR spectrum for H is shown in Fig. 1. The 1H NMR spectrum is shown in Fig. 2 together with a four-fold expansion of the region 6.5 – 7.1 ppm. The 1H NMR spectrum after the addition of a drop of D2O, is shown in Fig. 3. Peaks due to the solvent are marked with an asterisk (*).
5.5 Draw the structure of H.
5.6 Draw one resonance structure of phenol which explains the regioselective formation of H.
Model Answer
H
A second compound, I, is also formed in the reaction of phenol with acetone. The 13C NMR spectrum of I has 12 signals. The 1H NMR spectrum has the following signals: δ 7.50 – 6.51 (8H, m), 5.19 (1H, s), 4.45 (1H, s), 1.67 (6H, s); addition of D2O results in the disappearance of the signals at δ = 5.19 and 4.45
5.7 Draw a structure for I.
Excess phenol reacts with epichlorohydrin C in the presence of base to give compound L which has 6 signals in its 13C NMR spectrum. If the reaction is stopped before completion compounds J and K can also be isolated. Compound L is formed from compound K and compound K is formed from compound J.
5.8 Draw the structures of J, K and L.
Treatment of H with a large excess of epichlorohydrin C and base gives a mono-meric bis-epoxide M. M contains no chlorine atoms or OH groups.
5.9 Draw the structure of M.
Treatment of H with a small excess of epichlorohydrin and base gives N. N has the form: endgroup 1-n-endgroup 2 where n is approximately 10 – 15. N does not contain chlorine atoms and contains one OH group per repeat unit.
5.10 Draw the structure of N in the form indicated above:
(endgroup 1-n-endgroup 2).
5.11 Draw the repeat unit of the polymeric epoxy resin O formed from the reaction of the bis-epoxide M with ethane-1,2-diamine.