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9.4: Oxidation of Thiols

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    433013

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    Learning Objectives
    • The oxidation of thiols gives disulfides.

    Sulfur is in the same group (6A) of the periodic table as oxygen, the two elements have some similar properties. We might expect sulfur to form organic compounds related to those of oxygen, and indeed it does. Thiols, which are sulfur analogs of alcohols, have the general formula RSH. Methanethiol, has the formula CH3SH. Ethanethiol is the most common odorant for liquid propane (LP) gas.

    The oxidation of thiols are however very different from alcohols. Primary alcohols are oxidized to aldehydes and secondary alcohols are oxidized to ketones. Tertiary alcohols cannot be oxidized. The oxidation of thiols gives compounds called disulfides. Two thiol molecules are required for the oxidation to form the disulfide. The loss of a hydrogen atom by each thiol is evidence that oxidation has taken place. The biological oxidizing agent NAD+ removes the hydrogen atoms as shown in figure 9.4.1 with ethanethiol.

    Thiol Oxidation.png

    Figure \(\PageIndex{1}\): Oxidation of Thiols.

    The amino acid cysteine [HSCH2CH(NH2)COOH] contains the thiol functional group which can be oxidized as shown in figure 9.4.2. Disulfide linkages (–S–S–) between protein chains are extremely important in protein structure.

    disulfide.jpg

    Figure \(\PageIndex{2}\): Disulfide Bridge

    Thioethers or sulfides, are sulfur analogs of ethers, have the form general formula RSR′. An example is dimethylsulfide (CH3SCH3), which is responsible for the sometimes unpleasant odor of cooking cabbage and related vegetables. Note that methionine [CH3SCH2CH2CH(NH2)COOH] has a thioether functional group.

    Summary

    The oxidation of two thiol functional groups leads to the formation of the disulfide functional group. Disulfide linkages (–S–S–) between protein chains are extremely important in tertiary structure of the protein.

    Concept Review Exercises

    1. What is the functional group of a thiol? Write the condensed structural formula for ethanethiol.

    2. What is the functional group of a disulfide? Write the condensed structural formula for dipropyl disulfide.

    Answers

    1. SH; CH3CH2SH

    2. –S–S–; CH3CH2CH2SSCH2CH2CH3

    Exercises

    1. A common natural gas odorant is tert-butyl mercaptan. What is its condensed structural formula?

    2. Write the equation for the oxidation of ethanethiol to diethyl disulfide.

    Answer

    1. (CH3)3CSH

    This page titled 9.4: Oxidation of Thiols is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by Deboleena Roy (American River College).