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It is known that diazomethane can methylate various compounds with acidic hydrogens. Diazomethane is most well-known for the efficient synthesis of methyl esters from carboxylic acids. Clayden, Greeves, & Warren (2012) mention that it can also methylate phenols ($\ce {pK_a = 10}$), but not straight-chain alcohols ($\ce {pK_a = 16}$). The latter not being acidic enough. I was just wondering if nitroalkanes ($\ce {pK_a = 10}$) would be able to be methylated by diazomethane?

Reference

Clayden, J., Greeves, N., & Warren, S. (2012). Organic Chemistry (2nd ed.). New York : Oxford University Press Inc.

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  • $\begingroup$ Never seen this reaction - which doesn't mean there are not examples though $\endgroup$ – Waylander Nov 28 '18 at 12:16
  • $\begingroup$ That pKa value looks wrong to me, for simple nitroalkanes. I'm sure it is substantially higher for nitromethane, eg. ca. 17. $\endgroup$ – Organic Chemistry Explained Nov 28 '18 at 12:20
  • $\begingroup$ @OrganicChemistryExplained I am referring to the pka in water. $\endgroup$ – Tan Yong Boon Nov 28 '18 at 12:21
  • $\begingroup$ @OrganicChemistryExplained According to Clayden's, pka of nitromethane is indeed 10. $\endgroup$ – Tan Yong Boon Nov 28 '18 at 12:23
  • $\begingroup$ OK, it looks like the ~10 value may be in water, although I haven't been able to find the original ref, whereas the pKa is 17.2 in DMSO - JACS 1975, 97(24), 7006. Like @Waylander, I haven't seen this reaction. I suspect that if it is acidic enough in the right solvent to treat with diazomethane, it give O-methylation rather than C-methylation, and that O-methyl product may readily hydrolyse on workup or attempts at purification. Interesting question! $\endgroup$ – Organic Chemistry Explained Nov 28 '18 at 12:45

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