Triphenyl(3,4,5-trimethoxybenzyl)phosphonium chloride monohydrate

The asymmetric unit of the title salt, C28H28O3P+·Cl−·H2O, contains a benzyltriphenylphosphonium cation, a chloride counter-ion, and a water molecule of crystallization. The 3,4,5-trimethoxy substituents of the benzylic functionality are arranged with the 3,5-methyl groups lying approximately in the aromatic ring plane while the 4-methyl group is out of the plane.

The asymmetric unit of the title salt, C 28 H 28 O 3 P + ÁCl À ÁH 2 O, contains a benzyltriphenylphosphonium cation, a chloride counter-ion, and a water molecule of crystallization. The 3,4,5trimethoxy substituents of the benzylic functionality are arranged with the 3,5-methyl groups lying approximately in the aromatic ring plane while the 4-methyl group is out of the plane. H atoms treated by a mixture of independent and constrained refinement Á max = 0.31 e Å À3 Á min = À0.33 e Å À3
We thank Dr N. M. Boag (Salford University) for access to the diffractometer.

Comment
The 3,4,5-trimethoxyphenyl group is found in a number of natural products with antifungal properties such as Brittonin A and B (Asakawa et al., 1976), and central nervous system therapeutic properties such as Kadsurin (Mervič et al., 1977). A number of anticancer chalcones also contain this functionality (Lawrence et al., 2006); common synthetic routes to these products involve Wittig chemistry or Knoevenagel condensation reactions. The title compound is a Wittig precursor requiring deprotonation in the presence of a carbonyl compound.
The activity of the molecule classes above is believed to be related to the conformation of the 3,4,5-trimethoxyphenyl group relative to the other aromatic ring present. One aspect of this may be due to the disposition of the three methoxy groups, and the title molecule was chosen to provide a simple starting reference point for a more extensive study.
The structure obtained shows that O-C vectors are directed at 7, 81, and 8° to the phenyl ring plane for the 3,4, and 5-methoxy groups respectively.

Experimental
The title compound was obtained from 3,4,5-trimethoxybenzyl alcohol in two steps.
The alcohol (20 g, 0.1 mol) was dissolved in diethylether (200 ml) and cooled to 0°C. Thionyl chloride (15 ml, 0.21 mol) was added dropwise over thirty minutes and the solution was stirred for two hours. Water (120 ml) was added portionwise and the ether layer was separated. Extraction of the aqueous layer with diethylether (3 x 25 ml), combination of the ether fractions, drying over granular calcium chloride, and removal of the solvent under reduced pressure gave white microcrystalline 3,4,5-trimethoxybenzyl chloride in near quantitative yield.
The product from the first stage was mixed with triphenylphosphine (37.2 g, 0.115 mol). Addition of toluene (200 ml) and pump-purging with nitrogen gave a colourless solution which was heated under nitrogen at reflux temperature for thirty hours. The reaction mixture was allowed to cool to room temperature before being filtered under nitrogen. The white microcrystalline product was washed with petroleum ether and dried under reduced pressure (42.1 g, 72%).
Crystallization of a small sample by layering petroleum ether (40-60°C) onto a concentrated dichloromethane solution produced crystals suitable for the structure determination.

Refinement
H atoms bonded to the O atom were located in a difference map and refined with distance restraints of O-H = 0.84 Å, and with U iso (H) = 1.2U eq (O). Other H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93-0.96 Å and with U iso (H) = 1.2 (1.5 for methyl groups) times U eq (C).