Distillation greasing glass joints

It is often advisable to lubricate ground-glass joint surfaces with an extremely thin film of vaseline. This applies particularly to joints employed in assemblies for distillation under reduced pressure. For distillations under greatly reduced pressures or at very high temperatures it is essential to employ a special lubricant, e.g., silicone grease. 

Some simple apparatus, suitable for high vacuum distillation, are collected in Figs. 11, 26, 1-4. Fig. 11, 26, 1 represents an apparatus, which is particularly well adapted for solids the ground glass joint must be lubricated with a grease of negligible vapour pressure. Hickman s vacuum still is shown in Fig. 11, 26, 2 it is about 60 mm. in diameter. 

Manipulation. Since thionyl chloride attacks rubber, and since the usual reaction products are HCl and SO2, the reagent should be manipulated in all-glass apparatus with silicon grease on the glass joints, and provision should be made for entrainment of the gases. The best practice is to carry out the reaction in a round-bottomed flask fitted with a reflux condenser and drying tube and mounted in a hood the flask later can be fitted with an adapter for removal of excess thionyl chloride at the pressure of an aspirator on the steam bath and then for vacuum distillation of the product. Many workers employ thionyl chloride in large excess, but the evidence seems to show that no excess is needed in case the reaction is run at room temperature or if the mixture is refluxed under an efficient condenser cooled with water at 20° or below. 

The assembly (Fig. 5) is attached to a conventional vacuum line equipped with a distillation train.8"10 All stopcocks and ground-glass joints are lubricated with an inert, self-thickened, halocarbon grease, which is unaffected by bromine. Germane is best prepared... 

The product is distilled through an 18-in. Vigreux column. The fraction boiling between 115 and 116° at 735 mm. amounts to 65 per cent of the crude product. Since chromyl chloride reacts with stopcock grease and has a tendency to cause glass joints to stick, ground-glass apparatus is not recommended for this distillation. 

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