Synthesis of 1-bromohexane

Preparation of 1-bromohexane (n-bromohexane)

Preparation of 1-bromohexane (n-bromohexane)

Preparation of 1-bromohexane (n-bromohexane)

With cooling, 1 mole of the 1-hexyl alcohol is treated first with 0.5 mole of concentrated sulfuric acid and then with 1.25 mole of hydrogen bromide (in the form of the 48%, constant-boiling, acid), and the obtained mixture is boiled for 6 hours under reflux. Then it is steam-distilled and the 1-bromohexane is separated off in the separating funnel. The crude 1-bromohexane is twice shaken carefully with about one-fifth of its volume of cold concentrated sulfuric acid or the same volume of concentrated hydrochloric acid in the separating funnel to dissolve the dihexyl ether produced as a by-product. The crude 1-bromohexane is washed with water then it is freed from acid with sodium bicarbonate solution, washed again with water, dried over calcium chloride, and distilled through a 20-cm Vigreux column. The yield of 1-bromohexane is 80%, n20/D 1.448; mp.p −85 °C; b.p. 154-158 °C; d=1.176 g/mL at 25 °C.

Organicum. Practical Handbook of Organic Chemistry, by Heinz Becker, Werner Berger and Günter Domschke, Addison-Wesley Pub. Co, 195-196, (1973)

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  1. Shilpa Ghoderao

    Can the reaction proceed by taking 1-Hexanol in excess rather than HBr due to high cost of aq.HBr associated. ? if yes what % excess of alcohol?

    1. Post author

      It is not advisable to use an access of 1-hexanol as purification is more complicated. Moreover, side reaction leading to formation of n-hexyl ether could occur:

      C6H13Br + C6H13OH -> C6H13OC6H13

  2. Shilpa Ghoderao

    Could you suggest for an alternative solvent to di ethyl ether for extraction purpose due to hazards associated and difficulty in recovery.

  3. Shilpa Ghoderao

    Bromide ion is in aq HBr, How does it contact the organic alcohol phase?
    How cool should the concentrated sulphuric acid be for extracting the ether?

  4. Shilpa Ghoderao

    What is the purpose of refluxing?
    Which ether should be used to extract the product and In what quantity ?

  5. Shilpa Ghoderao

    What is the conversion of 1-hexyl alcohol? Some of the alcohol goes to form the main product which is 1-Bromohexane, some of it goes to by-product di-hexyl ether formation, what about the rest?? How to separate 1-hexyl alcohol and 1-Bromohexane as their boiling points are quite close and they are both miscible.

    1. Post author

      During the reaction 1-bromohexane should be obtained in as a major product. Side reactions could lead to di-hexyl ether, or some unsaturated products like hexene.

      The boiling point of 1-bromohexane is 154-158°C and unreacted 1-hexyl alcohol 156-157°C, meanwhile boiling point of di-hexyl ether is 228-229°C. Simple distillation could separate the 1-bromohexane and 1-hexyl alcohol as a mixture from di-hexyl ether. Further purification could be achieved by dissolving 1-bromohexane and 1-hexyl alcohol in ether and extracting 1-hexyl alcohol with weak alkaline solution (Na2CO3) according to following equation:

      CH3(CH2)5OH + NaOH (or Na2CO3) → CH3(CH2)5ONa + H2O

      CH3(CH2)5ONa is soluble in water, meanwhile 1-bromohexane remains in etheral solution.

        1. Post author

          Thank you for interest

          Usually in the scientific literature ether is referred to as diethyl ether and alcohol means ethyl alcohol. Otherwise, it is specified e.g n-dihexyl ether, dimethyl ether (or methyl alcohol, n-hexanol)

          Kind regards

  6. Shilpa Ghoderao

    What is the temperature maintained while addition of 48% HBr and at what temperature is the reactants mixture refluxed ?

    1. Post author

      Thank your for your interest.

      The original source does not provide your specified information. In general, the sulfuric acid should be added at room temperature or (if necessary with slight cooling), the same applies and for the 48% hydrobromic acid.
      The boiling point of the mixture will by >100°C as the boiling point of 1-hexanol 155-159 °C, hydrobromic acid 122 °C, 1-bromohexane 154-158 °C.

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