1-Bromobutane

The twenty one protocols found use four synthetic routes. Protocols A to Q use the reaction (AE = 50%)

CH₃CH₂CH₂CH₂OH + NaBr + H₂SO₄ → CH₃CH₂CH₂CH₂Br + NaHSO₄ + H₂O               (1)

protocol R uses the reaction (AE = 88%)

CH₃CH₂CH₂CH₂OH + HBr → CH₃CH₂CH₂CH₂Br + H₂O                                             (2)

both protocols S and T use the reactions (AE = 74%)

Br₂ + SO₂ + H₂O → 2 HBr + SO₃                               (AE = 70%)                         (3a)

CH₃CH₂CH₂CH₂OH + HBr → CH₃CH₂CH₂CH₂Br + H₂O  (AE = 88%)                           (3b)

and the protocol U uses the reaction (AE = 47%)

CH₃CH₂CH₂CH₂OH + KBr + H₂SO₄ → CH₃CH₂CH₂CH₂Br + KHSO₄ + H₂O                    (4)

The low atom economy values for reactions 1 and 4 are due to the fact that a sulphuric acid molecule is used to react with sodium or potassium bromide, respectively, to form the brominating agent and, as byproducts, sodium or potassium hydrogen sulphate; those reagents provide many atoms that are not incorporated into the product (the atom economy of the second reaction is smaller than that of the first because it uses the potassium cation, which has a higher atomic mass than sodium). Reaction 2 shows the highest atom economy because it uses directly hydrogen bromide as the brominating agent, from which only the hydrogen atom is not incorporated into the final product.

The third synthetic route (AE = 74%) is composed of two reactions: in reaction 3a (AE = 70%) the hydrobromic acid solution is prepared and works as the stoichiometric reagent of reaction 3b (AE = 88%). The decrease in the value of the atom economy in this route over the previous one is mainly due to the first reaction, since the sulphur dioxide, used to reduce the bromine to bromide, gives rise to the sulphur trioxide (byproduct), not supplying any atoms for the final product.