Phosphoric acid monoalkyl esters

It possesses surface-active properties in its acid form as well as in the form of its salts. In the case of 1 mol alcohol reacting with 1 mol phosphoric acid, a so-called primary or monoalkyl phosphoric acid ester with two remaining acid groups arises see Eq. (6). 

In addition to their poor solubility in water, alkyl phosphate esters and dialkyl phosphate esters are further characterized by sensitivity to water hardness [37]. A review of the preparation, properties, and uses of surface-active anionic phosphate esters prepared by the reactions of alcohols or ethoxylates with tetra-phosphoric acid or P4O10 is given in Ref. 3. The surfactant properties of alkyl phosphates have been investigated [18,186-188]. The critical micelle concentration (CMC) of the monoalkyl ester salts is only moderate see Table 6 ... 

The development of monoalkyl phosphate as a low skin irritating anionic surfactant is accented in a review with 30 references on monoalkyl phosphate salts, including surface-active properties, cutaneous effects, and applications to paste and liquid-type skin cleansers, and also phosphorylation reactions from the viewpoint of industrial production [26]. Amine salts of acrylate ester polymers, which are physiologically acceptable and useful as surfactants, are prepared by transesterification of alkyl acrylate polymers with 4-morpholinethanol or the alkanolamines and fatty alcohols or alkoxylated alkylphenols, and neutralizing with carboxylic or phosphoric acid. The polymer salt was used as an emulsifying agent for oils and waxes [70]. Preparation of pharmaceutical liposomes with surfactants derived from phosphoric acid is described in [279]. Lipid bilayer vesicles comprise an anionic or zwitterionic surfactant which when dispersed in H20 at a temperature above the phase transition temperature is in a micellar phase and a second lipid which is a single-chain fatty acid, fatty acid ester, or fatty alcohol which is in an emulsion phase, and cholesterol or a derivative. 

Monoalkyl phosphate and phosphate esters are special types of phosphoms-contain-ing anionic surfactants that are of great industrial importance. They are used for flameproofing, as antistatic for textiles, for foam inhibition, as an extreme pressure (EP) lubricant additive, as a surfactant component for alkaline, and as acid cleaners and for special cosmetic preparations (5). The commercially available phosphate ester products are complex mixtures of monoester and diester, free phosphoric acid, and free nonionic. 

The resulting product is a mixture of dialkyl and monoalkyl phosphate esters. These products also contain small amounts of condensed phosphates and phosphoric acid. Neutralization of the acids with bases like alkali hydroxides, ammonia, or amines produces water-soluble anionic surfactants and emulsifiers. 

In acidic solution, pliosphate esters are readily cleaved to phosphoric acid. In alkaline solution, however, only trialkyl phosphates, (RO)3PO, are hydrolyzed, and only one alkoxy group is removed. Monoalkyl and dialkyl esters, ROPO(OH)2 and (R0)2P0(0H), are inert to alkali, even on long treatment. This may seem unusual behavior, but it has a perfectly rational explanation. The monoalkyl and dialkyl esters contain acidic —OH groups on phosphorus, and in alkaline solution exist as anions repulsion between like charges prevents attack on these anions by hydroxide ion. 

Synthesis of Phosphoric Acids and Their Derivatives. - A series of monoalkyl and dialkyl phosphorus acid chiral esters have been synthesised for use as carriers for the transport of aromatic amino acids through supported liquid membranes. The compounds acted as effective carriers but enantio-separation was at best moderate. A range of phosphono- and phosphoro-fluoridates have been prepared by treatment of the corresponding thio- or seleno- phosphorus acids with aqueous silver fluoride at room temperature (Scheme 1). In some cases oxidation rather than fluorination occurred. Stereospecifically deuterium-labelled allylic isoprenoid diphosphates, e.g. (1), have been synthesised from the corresponding deuterium-labelled aldehyde by asymmetric reduction, phosphorylation and Sn2 displacement with pyrophosphate (Scheme 2). ... 

Kao [48] has reported an elaborate, extractive process to produce 96 wt% MAP containing only 2.3% phosphoric acid and <1% each of DAP and unreacted alcohol. The process uses a fivefold molar excess of polyphosphoric acid (105%) to alcohol, thereby minimizing unreacted alcohol in the product. Because of the high viscosity of the intermediate product, the reaction is carried out in hydrocarbon (hexane) solvent. On completion of the reaction, additional hexane is added and the mixtnre is extracted with isopropanol. The hexane and aqueous layers are then separated. The hexane layer containing the MAP ester is extracted for the second time with aqueous isopropanol, then any residual water and isopropanol are removed by azeotropic distillation with continuous hexane addition. The hexane fraction is cooled, allowing the monoalkyl ester to crystallize. It is filtered and the residual hexane is distilled for recycle. The water-isopropanol extracts containing phosphoric acid are then stripped to recover the phosphoric acid for recycle. This batch process can be adapted to a continuous operation. Several refinements of this process have been published [49-51]. 

Trade Names Arlatone MAP Concentrate Potassium C12-13 alkyl phosphate Synonyms Potassium Cl 2-13 monoalkyl phosphate Definition Potassium salt of a complex mixture of esters of phosphoric acid and Cl 2-13 alcohols... 

---