Pear combining with sulfur dioxide

The crude ester is cooled, an equal volume of benzene is added, then the free acid is neutralized by shaking with about 250 cc. of a 10 per cent solution of sodium carbonate (Note 4). The benzene solution is poured into 1300 cc. of a saturated solution of sodium bisulfite (about 60 g. of technical sodium bisulfite per 100 cc.), contained in a wide-neck bottle equipped with an efficient stirrer, and the mixture stirred for two and a half hours. The mixture soon warms up a little and becomes semi-solid. It is filtered through a 20-cm. Buchner funnel and carefully washed, first with 200 cc. of a saturated solution of sodium bisulfite, finally with two 150-cc. portions of benzene (Notes 5 and 6). The white pearly flakes of the sodium bisulfite addition product are transferred to a 3-I. round-bottom wide-neck flask equipped with a mechanical stirrer and containing 700 cc. of water, 175 cc. of concentrated sulfuric acid, and 500 cc. of benzene. The flask is heated on a steam bath under a hood, the temperature being kept at 55°, and the mixture is stirred for thirty minutes (Note 7). The solution is then poured into a separatory funnel, the benzene separated and the water layer extracted with a 200-cc. portion of benzene. The combined benzene solution is shaken with excess of 10 per cent sodium carbonate solution to remove free acid and sulfur dioxide (Note 8). The benzene is washed with a little water and then dried over anhydrous potassium carbonate (Note 9). The benzene is distilled at ordinary pressure over a free flame from a 500-cc. Claisen flask, the solution being added from a separatory funnel as fast as the benzene distils. It is advisable to distil the ester under reduced pressure although it can be done under ordinary pressure. The fraction distilling around n8°/5mm., 130710 mm., 138715 mm., 148725 mm., 155735 mm., or... 

The combined filtrates containing benzonitrile oxide are transferred to a 1-1. round-bottomed flask, treated immediately with 13.9 g. (0.1 mole) of N-sulfinylaniline added in one portion, with swirling, and set aside protected from moisture, while the temperature reaches a maximum of 33-34° (usually IS minutes). The mixture is then heated to reflux, protected from moisture, in a temperature-controlled oil bath for 3-5 hours. Continuous evolution of sulfur dioxide takes place during this period at the end of which the mixture is cooled and evaporated under reduced pressure (Note 3) at 70-80° to remove the solvent. The residual dark brown liquid is transferred to a 50-ml., pear-shaped distilling flask (Note 13) and heated, protected from moisture, at 110° for 30 minutes to complete the decomposition. It is then cooled and distilled under high vacuum (Note 14). Unchanged N-sulfinylaniline (2.0-2.5 g.) distills over at 45-50° (0.1-0.2 mm.). A second fraction (1.2-1.5 g.) is collected until the temperature reaches 112° (Note 15) then diphenyl carbodiimide is collected at 114-117° (0.1-0.2 mm.) as a clear yellow liquid yield 10.5-10.8 g. (54-56%) (Note 16) 1.6355 ... 

Miiller-Thurgau and Osterwalder (1914) suggested that the behavior of grape, pear, or apple juice could be explained by combination of the sulfur dioxide with some product of the fermentation. They presumed that this product was acetaldehyde, which since has been established as an intermediate in the metabolism of sugar by yeasts (Gortner, 1949). 

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