Chlorodiphenylphosphine is an organophosphorus compound with the formula (C6H5)2PCl, abbreviated Ph2PCl. It is a colourless oily liquid with a pungent odor that is often described as being garlic-like and detectable even in the ppb range. It is useful reagent for introducing the Ph2P group into molecules, which includes many ligands. Like other halophosphines, Ph2PCl is reactive with many nucleophiles such as water and easily oxidized even by air.[1]

Synthesis of Chlorodiphenylphosphine

Add 1.86mol phH and 0.9mol anhydrous AlCl3 to the dried four-necked flask with a stirrer, immediately install the reflux condenser and the exhaust receiver, and replace the air in the system with nitrogen. PCl3 0.9mol was added dropwise within 45 min with stirring. After the completion of the dropwise addition, the temperature is slowly raised until the reaction mixture is refluxed, and after the AlCl3 is completely dissolved, The temperature is raised to 140-150 ° C in 2 hours. Continue to react for 6 h in this temperature range. Cool to 35 ° C, add 1.8 mol of phosphorus trichloride to dilute it, Then add 0.96 mol of 2-methylpyridine dropwise at 25-40.Obtained a pale yellow viscous material, extracted with 500 ml of phosphorus trichloride each time, and continuously extracted several times. The solvent is distilled off under normal pressure, and the low-boiling substance is removed under reduced pressure to obtain 127.5 g of crude product of Chlorodiphenylphosphine. The fraction of 140-142 ° C was collected at 0.4 kPa to obtain a colorless viscous liquid of 95 g, and the yield of Chlorodiphenylphosphine was 47.50%. The infrared spectrum of the product chlorodiphenylphosphine was consistent with the standard infrared spectrum. The content of the gas was determined by gas chromatography to be >97%.[2]

Carbon nanotubes with chlorodiphenylphosphine

Covalent functionalization of multi-walled carbon nanotubes (MWCNTs) and oxidized MWCNTs (o-MWCNTs) with chlorodiphenylphosphine has been studied by cyclic voltammetry in organic medium. Depending the upper potential limit used in the electrochemical functionalization, different amount of phosphorus incorporation n is obtained, as result of the formation of radical species during the electrochemical oxidation of the Chlorodiphenylphosphine. The electrochemical oxidation of Chlorodiphenylphosphine promotes the covalent attachment of diphenylphosphine-like structure on the carbon nanotube surface. At the same time, the incorporation of Cl on the carbon nanotubes is observed during the functionalization. Furthermore, the presence of oxygen surface groups on the MWCNTs provides a favorable attachment of the Ph2P?+ species, whereas the amount of Cl is reduced.

In absence of Chlorodiphenylphosphine, MWCNTs present a quasi-rectangular voltammogram between 0 and 0.6 V with the absence of redox processes as corresponds to a double-layer capacitive behavior. The increase in the upper potential limit results in the appearance of redox processes as consequence of the oxidation of the MWCNTs surface at potentials higher than 0.7. Moreover, at higher upper potential limits, oxidation currents are clearly observed.[3]

In presence of Chlorodiphenylphosphine, an oxidation current with an on-set potential at around 0.45 V can be observed. The intensity of this oxidation current increases with the upper potential limit and it can be associated with the oxidation of Chlorodiphenylphosphine. Two oxidation processes at higher potentials are observed which do not have the corresponding reduction processes during the reverse scan. Electrochemistry of triphenylphosphine on vitreous carbon electrodes in acetonitrile has been studied in detail . It has been observed that the oxidation of triphenylphosphine shows an oxidation peak corresponding to the formation of a radical cation which can react with the residual water or other nucleophiles to produce triphenylphosphine oxide or the corresponding derivative. Then, according to this, the oxidation of Chlorodiphenylphosphine, that produces the A1 oxidation process at similar potentials as with triphenylphosphine.

On the other hand, the voltammograms obtained for MWCNTs-Chlorodiphenylphosphine-1.2 and MWCNTs-Chlorodiphenylphosphine-1.8 present a different behavior in comparison with the MWCNTs modified in absence of Chlorodiphenylphosphine. The MWCNTs-Chlorodiphenylphosphine-1.2 shows an increase in the peak potential separation (540 mV) indicating an increase in the irreversibility of the electron transfer (1.16x10?7 m s?1); however, the MWCNTs-Chlorodiphenylphosphine-1.8 shows an important decrease in the peak potential separation (160 mV) in comparison with the MWCNT-1.8 sample, which corresponds to an electrochemical rate constant of 1.3x10?5 m s?1, showing an improvement in the reversibility of the electron transfer kinetics. This can imply that during the electrochemical oxidation of the Chlorodiphenylphosphine at low upper potential limits the functionalities introduced in the MWCNTs produces a hindrance to the electron transfer; however, when the potential increases these functionalities can be removed by further oxidation, thus facilitating the electron transfer with values of peak potential separation close to the value obtained for pristine MWCNTs.

References

[1] Quin, L. D. A Guide to Organophosphorus Chemistry; Wiley IEEE: New York, 2000; pp 44-69

[2] SHANGHAI ZHENGPIN CHEMICAL - CN109956971, 2019, A

[3] Quintero-Jaime AF, Ghisolfi A, Cazorla-Amorós D, Morallón E. Electrochemical functionalization at anodic conditions of multi-walled carbon nanotubes with chlorodiphenylphosphine. J Colloid Interface Sci. 2022 Oct;623:915-926.