Benzyltriphenylphosphonium chloride

Maleic anhydride is a convenient dienophile because of its rapid reaction with most dienes as well as its stability and ease in handling (although it is poisonous). The diene for this reaction, 1,4-diphenyl-1,3-butadiene, is readily prepared by the Wittig reaction with benzyltriphenylphosphonium chloride and cinnamaldehyde (Chapter 11, Section I). 

The quaternary phosphonium salt is prepared by refluxing for 12 hours or longer a mixture of 4.5 g of benzyl chloride and 13 g of triphenylphosphine in 70 ml of xylene. On cooling to approx. 60°, colorless crystals of benzyltriphenylphosphonium chloride can be filtered off, washed with xylene (approx. 50 ml) and dried. The yield is virtually quantitative, mp 310-311°. 

In order to extend the reaction to further ketones, it was found by the group of Tian [119], that benzyltriphenylphosphonium chloride was a suitable phosphonium... 

Benzyltriphenylphosphonium chloride [1100-88-5] M 388.9, m 280° (sintering), 287-288 . Wash with Et20 and crystallise from EtOH (six sided plates). Hygroscopic and forms crystals with one mol H2O. [A 229 320 1885-, B 83 291 1950]. 

Benzonitriles have been synthesized by the reaction of nitric oxide (NO) with para-substituted benzyltriphenylphosphonium chlorides or bromides.64... 

Benzyltriphenylphosphonium chloride photodecomposes to yield radical products [153], while the corresponding tetrafluoroborate gives both radical products and an ionic product (the A-benzylacetamide in acetonitrile) the last type of compounds predominates with most of the substituted benzyl derivatives studied, except with 3- and 4-methoxy, while only radical products were formed upon triplet sensitization [154]. The 4-cyanobenzylphosphonium salt gave only radicalic products [155], but... 

A conductometric device for measurement of benzyltriphenylphosphonium ions was developed next [80]. Particles of benzyltriphenylphosphonium chloride-imprinted MAA-EDMA copolymer were held in a layer between two platinum wires using a filter paper. The device was exposed to the analyte in acetonitrile, an AC potential applied and the conductance recorded. The direct measurement principle is based on the enrichment of the analyte, a charged species, close to the electrode. A semi-linear response was observed between 1 mg/1 and 20 mg/1 (Fig. 18.4). In the two latter sensors it was anticipated that the effect of non-specific... 

Fig. 18.4, Conductivity of benzyltriphenylphosphonium ion-imprinted and non-imprinted polymer-based sensors in the presence of increasing concentrations of benzyltriphenylphosphonium chloride in acetonitrile.

Your instructor may ask you to prepare l,4-diphenyl-l,3-butadiene starting with commercially available benzyltriphenylphosphonium chloride. If so, start with Experiment 39B or 39C. The sodium ethoxide solution used in Experiment 39B must be kept tightly stoppered when not in use because it reacts readily with atmospheric water. Fresh cinnamaldehyde must be used in this experiment. Old cinnamaldehyde should be checked by infrared specfroscopy fo be cerfain that it does not contain any cinnamic acid. 

If your insfrucfor asks you to prepare benzyltriphenylphosphonium chloride in Experiment 39A, you can conduct another experiment concurrently during the 1.5-hour reflux period. Triphenylphosphine is rafher toxic. 

In the following operations, cap the 5-mL conical vial whenever possible to avoid contact with moisture from the atmosphere. If you prepared your own benzyltriphenylphosphonium chloride in Experiment 39A, you may need to supplement your yield in this part of the experiment. 

Place 0.480 g of benzyltriphenylphosphonium chloride (MW = 388.9) in a dry 5-mL conical vial. Add a magnetic spin vane. Transfer 2.0 mL of absolute (anhydrous) ethanol to the vial and stir the mixture to dissolve the phosphonium salt (Wittig salt). Add 0.75 mL of sodium ethoxide solution to the vial using a dry pipette while stirring continuously. Cap the vial and stir this mixture for 15 minutes. During this period, the cloudy solution acquires the characteristic yellow color of the ylide. 

Design and implement an experimental protocol for performing the reaction of Equation 18.8. Because 9-anthraldehyde is relatively expensive, you should plan to carry out the reaction at the microscale level unless instructed to do otherwise. You should be sure that your proposal includes a means to analyze for the possible presence of both isomeric products in the reaction mixture. Appropriate quantities of reagents are 0.97 g of benzyltriphenylphosphonium chloride (4), 0.57 g of 9-anthraldehyde, and 1.5 ml of 50% (by mass) of aqueous sodium hydroxide solution. Use 2-propanol as the solvent for recrystallizing the crude product. 

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