Mysterious Decomposition of Alkoxyphosphonium Chlorides: Postulated Involvement of the HCl₂ Anion and Its Capture in the Solid State

Abstract

P-Alkoxyphosphonium (AP) chlorides were generated by reacting P-chlorophosphonium chlorides with alcohols. Their well-known spontaneous Arbuzov-type collapse leading to phosphine oxides was studied and its rate found to be dependent on a number of factors in an unexpected fashion: it is inversely proportional to the initial concentration and it shows strong dependence on the acidity of the media but is not very sensitive to the presence of base. To explain these observations, we evoke a self-inhibition model with the formation of the less nucleophilic hydrodichloride anion HCl in solution. Detailed analysis of the kinetic data yields the association constant (K=3×10 m ) of the putative HCl species in chloroform. Experimental observations for the collapse of highly enriched diastereomeric alkoxyphosphonium (DAP) chlorides are fully analogous to the achiral AP also implying the involvement of HCl anions. Moreover, crystallisation of a highly enriched DAP salt derived from (-)-menthol furnished, for the first time, crystals of individual (R )-DAP hydrodichloride as confirmed by X-ray diffractometry. Importantly, the P-configuration and detailed conformation of the DAP moiety is in good agreement with DFT-level computational results. The thermal collapse of (R )-DAP⋅HCl proceeds with complete retention of the P-configuration furnishing the phosphine oxide of exceptional enantiomeric purity.

Synthesis of Decorated Carbon Structures with Encapsulated Components by Low-Voltage Electric Discharge Treatment

“…Hydrogen chloride, which appears in the spectrum and is retained during desorption to a temperature of 400 K, is apparently bound in the structures into a complex anion with triphenyl(chloromethyl)phosphonium chloride (reaction ( 5)) [34,35]. (5) Triphenylphosphine oxide is most likely formed as a result of the oxidation of PPh 3 with atmospheric oxygen during drying of the solid phase after the pulse low-voltage discharge treatment.…”

“…The thermal desorption spectrum of the solid products of polycondensation of the CHCl 3 + PPh 3 system shows that the main products are triphenylphosphine, triphenylphosphine oxide, and triphenylchloromethylphosphonium chloride. The products also contain hydrogen chloride, which is retained in solid products up to a temperature of 850 K. This anomaly in the behavior of HCl, according to [34], is due to the binding of HCl to the complex anion (reaction ( 5)). The use of triphenylphosphine as an activating component in the conversion of chloromethanes makes it possible to produce highly demanded chlorinated products that are difficult to obtain by other methods [35].…”

“…Comparison of the thermal desorption spectra of the solid products of polycondensation of CHCl 3 and CHCl 3 + PPh 3 shows that only perchlorinated hydrocarbons with different backbones (linear, cyclic, aromatic) are found in the former case. During the polycondensation of the binary system CHCl 3 + PPh 3 , the spectra show CHCl 3 ; C 6 Cl 6 ; triphenyl(chloromethyl)phosphonium chloride; and, additionally, HCl, which is released in the temperature range of 450-850 K. The thermal desorption analysis of the solid polycondensation products of the CH 2 Cl 2 + PPh 3 system also reveals the intense evolution of hydrogen chloride in the range of 360-800 K. The delay in the appearance of HCl is caused by binding Clto the complex anion Heating during the analysis of polycondensation products of the CH 2 Cl 2 + PPh 3 and CHCl 3 + PPh 3 systems results in slowly decomposition of the complex of triphenyl(chloromethyl)phosphonium chloride with the solid anion to form HCl [34]. The thermal desorption spectrum of the solid product of polycondensation of the CCl 4 + PPh 3 system exhibits an abnormality associated with a high benzene release temperature (997 K).…”

Development of a More Sustainable Appel Reaction

“…Either CPS formation was inhibited or Arbuzov collapse of the intermediate alkoxyphosphonium species was occurring very slowly, though no alkoxyphosphonium intermediates were observed by 31 P NMR. The relationship between Arbuzov collapse and pH has been investigated by Gilheany et al Thus, it was decided to add 0.2 equiv of Hünig’s base to the reaction mixture, premixed with PPh 3 O, as per Table , entry 3; an improvement from 21 to 50% chloride was observed. Following on from this result, the Hünig’s base was instead premixed with the benzyl alcohol and added together via the same syringe giving an excellent result of 95% chloride by HPLC (entry 4).…”

Quaternary Phosphonium Carboxylates: Structure, Dynamics and Intriguing Olefination Mechanism

“…In our earlier work on the chemistry of phosphonium IP species, we focused on structure featuring halogen bonding, 7 their dynamic self-exchange 8 and their key role in Arbuzov-type transformations. 9 Despite the fact that quaternary phosphonium cations (QPC) have a prominent role in the area of IP chemistry, 10 the respective tautomerisation process (Scheme 1, B) leading, via the stage of molecular complex 7, to ylides 8 has been explored relatively poorly, although experimental 11 and theoretical 12 findings pointed to the possibility of ylide formation directly from QPC salts. In this context, we note the elegant work of Perosa and coworkers 13 who demonstrated in practice the efficient vinylation with an IP reagent comprising of Ph 3 P-CH 3 + cation and methyl carbonate CH 3 OCOOanion.…”