3-({[(1-Phenylethyl)sulfanyl]methanethioyl}sulfanyl)propanoic acid

In the title compound, C12H14O2S3, a chain transfer agent (CTA) used in polymerization, the dihedral angle between the aromatic ring and the CS3 grouping is 84.20 (10)°. In the crystal, carboxylic acid inversion dimers linked by pairs of O—H⋯O hydrogen bonds generate R 2 2(8) loops.


Comment
The title compound C 12 H 14 S 3 O 2 is a carbanotrithioate. It can be used as a chain transfer agent (CTA) in RAFT polymerization (Chong et al., 1999) to control the polymerization and it will produce carbanotrithionate end-terminated polymers.
Very few single-crystal XRD data are available for CTAs, because most of them are liquids (Coady et al., 2008). Recently, we have reported the single-crystal data of a multi-functional CTA, which can be used for the synthesis of star polymers.
Carbanotrithioate CTA is suitable for the polymerization of styrene, acrylates and methacrylates. With appropriate choice of the CTA (RAFT agent) and reaction conditions, RAFT polymerization can be successfully used to produce polymers of narrow polydispersity with predetermined molecular weights. Moreover, the polymers obtained by the RAFT process can be chain extended or used as precursors to synthesize stimuli responsive block copolymers by the addition of further monomer(s). The title compound will result in carboxylic acid end-terminated polymer; this functionality can be further modified and utilized for making block copolymers by reacting it with another homo-polymer.
The compound C 12 H 14 S 3 O 2 is stabilized by a O-H···O interaction with R 2 2 (8) graph set motif.

Experimental
The title compound, was prepared by adding 3-mercapto propanoic acid (1.00 g, 7.35 mmol) to a stirred suspension of K 3 PO 4 (1.72 g, 8.09 mmol) in acetone (20 ml) over a period of ten minutes. CS 2 (1.68 g, 22.06 mmol) was added upon which the solution turned bright yellow. After stirring for ten minutes 1-bromo ethyl benzene (1.26 g, 7.35 mmol) was added and an instant precipitation of KBr was noted. After stirring for three hours the suspension was filtered and the cake was rinsed with acetone (2 × 20 ml). After removing the solvent from the filtrate under reduced pressure the resulting yellow residue was purified by column chromatography on silica using a petroleum ether/ethyl acetate gradient to yield light yellow solid (96%) that crystallized to form light yellow blocks.

Refinement
All hydrogen atoms were fixed geometrically and allowed to ride on the parent carbon atoms, with aromatic C-H = 0.93 Å, methyl C-H = 0.96 Å and methylene C-H = 0.97 Å. The displacement parameters were set for phenyl and methylene H atoms at U iso (H) = 1.2U eq (C) and methyl H atoms at U iso (H) = 1.5U eq (C).