Solvents Boiling Above 100°C Which Have an Azeotrope with Water Boiling Less than 100°C

Solvent	Boiling Point  (bp)	Azeotrope (bp)	% Water
Nitromethane	101.2	83.6	24
Pentachloroethane	162	95.9	--
1,1,2-Trichloroethane	113.8	86	16.4
Nitroethane	114	87	28
Dimethylsulfate	189	98.6	73
Epichlorohydrin	115	88	25
Methylchloroacetate	131	93	36
1-Chloro-2-propanol	127	95	46
1-Nitropropane	131	92	36
2-Nitropropane	120	89	29
Propylnitrate	110	85	25
Pyrazine	114	96	40
2-Ethoxyethanol	135	99.4	70
1-Methoxy-2-propanol	118	96	49
2-Methoxy-1-Propanol	130	98	67
Pyridine	115	94	41
Cyclopentanone	130	95	42
Cyclopentanol	141	96	58

A convenient property of solvents is that they have low boiling points. There are common solvents with boiling points above 100°C but their frequent use is usually because of some special properties and rather in spite of their high boiling points. In the table above I list less common solvents that are relatively high boilers but have the advantage that they possess an azeotrope with water that can distill at less than 100°C. Perhaps if this is more widely known they will get more usage.

Of these, pentachloroethane is toxic and does not seem to have any compensating virtue.

1,1,2-trichloroethane may be useful as an extraction solvent because it is more likely to be the more dense, lower layer in a liquid-liquid extraction. The lower phase is more convenient to remove from the reactor. Even as a cosolvent for extracting lipophilic materials it is likelier to give a lower layer.

Dimethylsulfate was used as a chemical weapon in WW1. It is a potent methylating agent. The first methyl is transferred to nucleophiles much more easily than the second. Although Wikipedia says that it reacts with water, this rate of reaction is not particularly consequential if it occurs at all. It can be steam-distilled and forms an azeotrope with water as you can see in the table. It can be used in excess for methylations since the excess can be removed as an azeotrope with water.

Both pyridine and pyrazine are miscible with both water and organic solvents yet they can be extracted into water as salts with such acids as oxalic, citric, or tartaric.