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Topic: Synthesis of tetrahydrothiophene  (Read 5485 times)

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Offline prophecy

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Synthesis of tetrahydrothiophene
« on: June 02, 2008, 09:51:13 AM »
4-bromobutane-1-thiol in the presence of a strong base such as NaH (sodium hydride, hydride [H-] is the base) will give an SN2 mechanism and produce tetrahydrothiophene, 99% of the time.

Although, 1% of the time you'll make but-1-ene-4-thiol. Can someone explain to me why, and explain how the mechanism works. I know how tetrahydrothiophene's mechanism, but not the but-1-ene-4-thiol. If someone could help, I'd appreciate it.

Thanks!

Offline macman104

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Re: Synthesis of tetrahydrothiophene
« Reply #1 on: June 02, 2008, 09:55:25 AM »
E2 mechanism.  Instead of deprotonating the thiol, take a hydrogen from the carbon adjacent to the bromine and do an E2 elimination.

Offline spirochete

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Re: Synthesis of tetrahydrothiophene
« Reply #2 on: June 02, 2008, 11:16:15 PM »
Except that NaH happens to be insoluble in organic solvents and is therefore incapable of taking part in SN2 reactions.  Its insolubility makes this form of hydride ion the most sterically hindered nucleophile possible,

Offline macman104

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Re: Synthesis of tetrahydrothiophene
« Reply #3 on: June 03, 2008, 07:39:37 PM »
Except that NaH happens to be insoluble in organic solvents and is therefore incapable of taking part in SN2 reactions.  Its insolubility makes this form of hydride ion the most sterically hindered nucleophile possible,
Um...I don't think anyone was talking the hydride acting in an SN2 manner.  In addition, the reaction you propose wouldn't give the target compound.  Instead NaH is a very strong base such that it can deprotonate the thiol group, which CAN perform SN2 chemistry.

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