7. The bp of the product is
130°C
at 1 mm. An
oil bath temperature of 160-170°C is necessary
to achieve rapid distillation. Temperatures above 190°C lead to decomposition,
although a bath temperature of 200°C and the use of a
heat gun
at the end might be necessary to transfer the distillate completely into one receiver
flask. Moreover, vigorous stirring during distillation is advisable, since the compound
tends to delayed boiling.
8. The distillate is pure by elemental analysis and is free from
solvent contamination. The physical properties are as follows: C
12H
18O
4
(226.27): Anal. Calcd for C, 63.70; H, 8.02. Found C, 63.48; H, 7.93; Mol. mass calcd.
226.1205, found 226.1207 (HRMS). Spectral data: IR
(ATR) cm
−1: 2976 (m), 1748 (vs), 1717
(vs), 1448 (m), 1406 (m), 1367 (m),
1318 (m), 1260 (s), 1232 (s), 1165 (s),
1116 (m), 1029 (m), 861 (m);
1H NMR (400 MHz, CDCl
3)
δ: 1.23 (t, 3 H, J = 7.2), 1.82 - 2.03 (m, 4 H), 2.03
- 2.13 (m, 1 H), 2.12 (s, 3 H), 2.24 - 2.49 (m, 4 H),
2.69 (ddd, 1 H, J = 18, J = 9.6, J = 6.0), 4.14 (q, 2 H, J = 7.1);
13C NMR (50 MHz,
CDCl
3) δ: 13.29 (CH
3), 18.84 (CH
2),
26.24 (CH
2), 29.00 (CH
3), 33.22
(CH
2), 37.07 (CH
2), 38.01 (CH
2),
58.23 (C), 60.23 (OCH
2), 170.47 (C=O),
206.61 (C=O), 213.75 (C=O).
9. As an alternative to distillation and in accord with the observations
of the submitter, the checkers have shown that the reaction mixture can be diluted
with
100 mL of methyl t-butyl
ether (MTBE), and filtered through a column of
150
g of silica gel with sufficient flushing by MTBE to remove all product.
Concentration of the MTBE on a
rotary evaporator followed by
keeping the resulting oil at 1 mm/25o for 24 hr affords product of comparable purity,
except for traces of MTBE, and slightly improved yield.