Submitted by C. S. Marvel and H. O. Calvery.
Checked by H. T. Clarke and M. R. Brethen.
1. Procedure
A
100-cc. round-bottomed, wide-mouthed flask (or a
large test tube 18 cm. long and 4.5 cm. wide) is fitted with a
rubber stopper carrying a
separatory funnel, a
thermometer, an
inlet tube reaching almost to the bottom of the flask, and an
outlet tube leading to a
condenser set for downward distillation. A
receiver consisting of a suction flask is attached tightly to the end of the condenser, and the side arm of the receiver is attached to a
reflux condenser. A tube is led from the top of the condenser to the
hood in order to take care of excess
hydrogen chloride during the distillation, or a
gas-absorption trap (Fig. 7, p. 97) can be used for this purpose. About
25–30 cc. of trimethylene glycol (b.p.
210–215°) is placed in the flask and heated by means of an
oil or metal bath to 150–170°. A
very rapid stream of dry
hydrogen chloride (Note
1) is now led into the hot glycol through the inlet tube. A reddish distillate consisting of water,
trimethylene chlorohydrin,
hydrogen chloride, and some unchanged glycol begins to distil. As rapidly as the glycol is used up in the reaction flask, more is added from the separatory funnel. It is always advisable to keep the amount of material in the reaction flask as small as possible. The rate at which the
hydrogen chloride is passed through the flask controls the reaction and also has a marked effect on the yield (Note
2). The best results are obtained by passing in the gas rapidly enough to use up
2–3 cc. of trimethylene glycol in one minute. The process is continuous and can be run indefinitely without changing the apparatus. The weight of crude distillate from
1800 g. of trimethylene glycol is usually
2300–2500 g.
To obtain the
trimethylene chlorohydrin, the distillate from this operation is heated for about one hour on a
steam bath in order to drive out most of the excess
hydrogen chloride. The distillate is then fractionated under reduced pressure (Note
3) in a
modified Claisen flask (p. 130). The
fractionating side arm should be 25 cm. in length. The fractions collected under 10 mm. are: to 55°, 55–57°, 57–65°, 65–85°, 85–105°, residue.
Before a further fractionation is carried out, the residue is discarded; the portion boiling at
85–105°, consisting chiefly of unchanged
trimethylene glycol, is set aside for use in a later preparation; the low-boiling portion up to 55°, consisting mainly of water and
hydrogen chloride with some
trimethylene chloride (Note
4) and
trimethylene chlorohydrin, is neutralized carefully with powdered
sodium carbonate. Two layers form, and the upper containing the chlorohydrin is separated, dried over anhydrous
potassium carbonate, and again replaced as the portion boiling up to 55°. Another complete fractional distillation, carried out in the usual way, is now made except that the highest fraction boils at 65–85°/10 mm.
2. Notes
2. The yield of chlorohydrin is largely determined by the rate at which the reaction is carried out. A very rapid stream of
hydrogen chloride is absolutely essential for obtaining the yields mentioned. Moreover, it is very important to keep as small an amount of glycol as possible in the reaction flask. If larger amounts of glycol are present at any one time, the yield of product is lowered and considerable tar is produced.
3.
Trimethylene chlorohydrin cannot be distilled under atmospheric pressure without some decomposition. The fractionation can be carried out at ordinary pressures when the fractions collected are up to 125°, 125–158°, 158–164°, 164–190°, 190–210° and residue. This procedure is less desirable as some
hydrogen chloride is evolved and the product turns dark on standing.
4. The portion boiling up to 55°/10 mm., obtained after the second fractionation, was washed with concentrated
sulfuric acid, then water, and finally dried and distilled. A certain amount of
trimethylene chloride was sometimes obtained, boiling at
115–120° and amounting to about 30 per cent of the total fraction.
3. Discussion
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