A primary alkyl halide may also undergo SN1 reaction in aqueous formic acid.
This statement is written in one of my organic textbooks. Is it true ?
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$\begingroup$ What do you think? $\endgroup$– WaylanderCommented May 30, 2019 at 13:24
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$\begingroup$ I don't know. It was written in one of the reputed organic chemistry textbooks. I think It can be true. But How ? $\endgroup$– PrakharCommented May 30, 2019 at 13:26
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$\begingroup$ SN1 and SN2 are selected according to the stability of halogenated hydrocarbons corresponding to carbon cations, and have little relationship with reagents. $\endgroup$– Liddy NieCommented May 31, 2019 at 6:38
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$\begingroup$ If you're asking in a general sense, then no. Primary alkyl halides generally prefer SN2, over SN1 since it (generally - for primary halides) takes less activation energy to do the substitution in a concerted way, rather than a relatively unstable primary carbocation. But, if you (or your textbook) is more interested in some relatively rare example of some perfluorinated substrate using very poor nucleophiles that is almost fully solvated in aqueous formic acid, then maybe it's true. Please could you provide us with the reference of the reputed textbook so that we can see the context? $\endgroup$– ZachrCommented Jun 2, 2019 at 2:15
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Quoting ORGANIC CHEMISTRY SECOND EDITION ,Jonathan Clayden ,Nick Greeves , Stuart Warren from page no.338 ,in 50% aqueous ethanol the values give you an idea of the relative reactivity towards substitution of the different classes of compound. These rates are mostly SN1, but there will be some SN2 reactivity with the primary compounds.
And in page 342 ,the rates of reaction of the following alkyl chlorides with KI in acetone at 50 °C broadly illustrate the patterns of SN2 reactivity are analysed. These are relative rates with respect to n-BuCl as a ‘typical primary halide’.
As you have not mentioned any alkyl halide,n-butyl chloride's relative rate of reaction is 0.07 in 50% aqueous ethanol.Its tendency to undergo SN2 is more then SNI.
Similarly a primary alkyl halide in acetone at 50 °C has greater tendency towards SN2.
answered May 30, 2019 at 13:50