The Reed reaction is a chemical reaction that utilizes light to oxidize hydrocarbons to alkylsulfonyl chlorides. This reaction is employed in modifying polyethylene to give chlorosulfonated polyethylene (CSPE), which is noted for its toughness.^[1]

Commercial implementations

Polyethylene is treated with a mixture of chlorine and sulfur dioxide under UV-radiation. Vinylsulfonic acid can also be prepared beginning with the sulfochlorination of chloroethane. Dehydrohalogenation of the product gives vinylsulfonyl chloride, which subsequently is hydrolyzed to give vinylsulfonic acid:

ClCH₂CH₃ + SO₂ + Cl₂ → ClCH₂CH₂SO₂Cl + HCl

ClCH₂CH₂SO₂Cl → H₂C=CHSO₂Cl + HCl

CH₂=CHSO₂Cl + H₂O → H₂C=CHSO₃H + HCl

Mechanism

The reaction occurs via a free radical mechanism. UV-light initiates homolysis of chlorine, producing a pair of chlorine atoms:

Chain initiation:

${\displaystyle {\ce {Cl2 ->[h\nu] 2Cl.))}$

Thereafter a chlorine atom attacks the hydrocarbon chain, freeing hydrogen to form hydrogen chloride and an alkyl free radical. The resulting radical then captures SO₂. The resulting sulfonyl radical attacks another chlorine molecule to produce the desired sulfonyl chloride and a new chlorine atom, which continues the reaction chain. Chain propagation steps:

${\displaystyle {\ce ((R-H}+ .Cl -> {R.}+ HCl))}$

${\displaystyle {\ce ((R.}+{:}SO2->R-{\dot {S))O2))}$

${\displaystyle {\ce ((R-{\dot {S))O2}+Cl2->{R-SO2-Cl}+Cl.))}$