Sorry to dig up an old post but I figured I'd share some recent (partial) success and also ask for advice.
So I've been trying to make dimethyl sulfate. I figured I'd start with Painkilla's excellent text document. I tried the reaction on half the scale.
The sodium sulfate was well dried and finely powdered, and added to the mixture of methanol and sulfuric acid. The appearance of the mixture changed
gradually over time, becoming more opaque (white?) and thick, almost with the appearance of how I'd imagine a fine chalk suspension to look. Leaving
this for a couple of hours (2 hours), it was allowed to settle for a little time (I had little patience though it helped very little). A glass
sintered funnel (por 3) and buchner flask were dried with a heat gun under evacuation, left to cool, and the mixture filtered (under full vacuum,
about 20mbar). This took OVER AN HOUR due to the fine nature of the sodium sulfate.
100g of the methylsulfuric acid* were transferred to a dried 100ml RBF and the appropriate amount (22.5g according to Painkilla's document) of finely
powdered anhydrous sodium sulfate was added with vigorous magnetic stirring. The thick suspension was placed under high vacuum (0.5mbar) for a few
minutes, and then a bleed was introduced via another tap on the schlenk line, bringing the system pressure to 10mbar. Heating was commenced, and
strong bumping began at a bath temperature of 95*C. At a bath temperature of 120*C, distillate began to pass over, and the evolution of distillate
increased at a bath temperature of 145*C. Heating was maintained and increased as the amount of distillate dwindled. A final temperature of 200*C
(vapour temperature of 120*C). A biphasic mixture was obtained, which was poured into a measuring cylinder, the upper layer removed, a volume of water
added, agitated, and removed, leaving 11ml of slightly milky dimethyl sulfate (a 25% yield) which was dried over anhydrous magnesium sulfate.
A subsequent run was made using 20g anhydrous magnesium sulfate to dry the mixture of methanol and sulfuric acid, and no additive during the
distillation. 83g of methylsulfuric acid was obtained on filtration (less than before) and on distillation at a pressure of ~25mbar gave a biphasic
mixture yielding 7ml dimethyl sulfate after washing. The bath temperatures more closely match what Painkilla describe though, and the distillation in
practice was "easier" (for want of a better description). In total I now have 18ml of crude dimethyl sulfate.
However, I wish to still accumulate and find a better method of preparing it. The distillations take an hour or two each, but the clean up after takes
longer, carefully dismantling the appratus and placing each piece in a base bath and leaving it there for a few hours (overnight) to hydrolyse any
dimethyl sulfate. I've thought about possible problems and my main concern is with the preliminary drying step. When adding the magnesium sulfate (a
much more rapid drying agent), it initially clumped together, but it appears to have been ground to a fine powder by the mag stirrer bar. I think if I
were to try this again, the mag stirring would be cut off before addition of solid.
I'm also interested in trying the CuCl2/SO2 method, as I feel this would be fruitful, especially if it can be easily adapted to produce diethyl
sulfate. I feel the troubles lie in the workup of the reaction mixture, so any advice here is welcomed.
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