Effect Of Phosphorylation Reaction On Leather

Abstract: the common ways of phosphorylation are discussed. Phosphoric acid method The azeotropic dehydration method, phosphorus pentoxide / phosphoric acid method, powdered addition of phosphorus pentoxide and solvent addition method are briefly introduced. The composition analysis methods and problems of phosphate esters are briefly described. The research status of synthetic phosphate esters in leather fatliquoring is introduced. It is pointed out that in order to better improve the fatliquoring performance of phosphate fatliquoring agents, the molecular design of phosphate esters should be designed from the leather industry's requirements for multifunctional and greening of fatliquoring agents.

Key words: phosphorylation reaction; composition analysis; phosphate fatliquoring agent

Chinese map classification number: TS529.4 document identification code: B article number: 1004-8960 (2005) 02-0027-04

Phosphate is an important surfactant. It is widely used in chemical fibers. Spin , plastics, paper making, Leatherwear And daily chemicals. The introduction of phosphoric acid into organic compounds can endow organic compounds with unique properties, such as antistatic property, emulsifying dispersion, bactericidal property, low irritation, low toxicity, chemical stability and biodegradability. [1-5]

Phosphates are synthesized by phosphorylation. Phosphorylation is the esterification reaction of hydroxyl compounds (such as fatty alcohols, alkylphenols, oils, etc.) with phosphorylation agents. Phosphorylation plays an important role in the preparation of new leather fatliquors.

1 commonly used methods for preparing leather fatliquors by phosphorylation reaction

1.1 polyphosphoric acid method

Polyphosphoric acid is mostly prepared by phosphoric acid and phosphorus pentoxide in water and water. The method is characterized by high stability of raw material polyphosphoric acid, convenient proportioning and metering, easy process control, no exhaust gas and waste liquid discharge, and wide industrial application prospect [6]. Polyphosphoric acid can be prepared by the following methods: according to the measurement requirements, 85% phosphoric acid and phosphorus pentoxide can be added into the cone bottle, and a thermometer and a 40cm long condensation glass tube are inserted on the bottle stopper. After plugging on the conical bottle, the five oxidation and two phosphorus can be dissolved by magnetic heating and stirring. After the solution is transparent, the solution is decolorized with appropriate amount of hydrogen peroxide, and then heated to about 210 degrees Celsius for a long time to cool. Phosphoric acid concentration is expressed by percentage of phosphorus pentoxide. Wang Qingcheng and others studied the phosphoric acid and sixteen alcohol content of 79.98% pentoxide pentoxide under solvent-free condition. The yield of phosphate monoester was 93.4%, the total yield of phosphate was 94.5%, and the ratio of mono diester phosphate was 99%.

1.2 azeotropic dehydration

This method mainly uses phosphoric acid as phosphorylation reagent, and can be divided into two kinds of [7], non solvent azeotropic dehydration and solvent azeotropic dehydration. In the case of dehydration, phosphoric acid is highly reactive and can be directly esterified with hydroxyl compounds. In the reaction system of preparing phosphate with ROH and H3PO4, besides the direct esterification of phosphoric acid is the main reaction, there are many other reactions, such as alcoholysis or hydrolysis of pyrophosphate and pyrophosphate bonds. When Superacid is used as catalyst, these reactions can be carried out at the acid active center of the catalyst. Due to the change of reaction pathway, the activation energy decreases, and the phosphorylation rate of ROH increases obviously.

Heakazaki [7] et al. Reported the research results of the development of high purity phosphoric acid monoester with phosphoric acid and twelve alcohol in the solvent boiling process of xylene solvent.

The relationship between the rate of dehydration and the rate of product formation was studied in depth by 31NMR. Thus exploring the mechanism of direct phosphorylation of ROH with phosphoric acid: ROH acts as a nucleophile to attack PA directly from the back, which is a nucleophilic substitution reaction that follows the SN2 process. On this basis, he wen Meng [8] and others discussed the phosphorylation reaction of phosphoric acid and eighteen alcohol in different solvents by azeotropic dehydration. The influence of super acid (SO2-4/MxOy) as catalyst on the reaction was investigated. It was found that the reaction rate could be doubled by the use of catalyst. It was considered that using solid superacid as catalyst, the proton acid or Lewis acid active center existed on the surface of the catalyst, which could adsorb PA to the acid center and greatly increase its reactivity. The nucleophilic substitution effect of ROH on phosphorus atoms became much easier. The mechanism may be the process of phosphorylation through adsorption, surface reaction and desorption.

1.3 phosphorus pentoxide / phosphoric acid method

[9] is added first by adding phosphoric acid, then adding phosphorus pentoxide in batches or directly mixing phosphorus pentoxide and phosphoric acid. Zhang Tingyou and others used the direct mixing of phosphorus pentoxide and phosphoric acid and the reaction of mixed alcohols to prepare alkyl phosphate waterproof fatliquoring agent. Guo Zhen Chu [10] et al. Used phosphoric acid and batch addition of phosphorus pentoxide to prepare ester phosphate castor oil phosphate. The method can increase the content of MAP and reduce the cost of raw materials because of the introduction of phosphoric acid. However, the content of inorganic salt in the product is higher, and the effective content of the reagent is difficult to measure.

1.4 powdered phosphorus pentoxide addition method

P2O5 is the most widely used and most important phosphorylation reagent in the preparation of phosphate fatliquoring agents. However, it should be known that the reaction between phosphorus pentoxide and hydroxyl compounds is exothermic reaction and liquid solid mass transfer process. Taking into account the influence of the melting point and purity of hydroxyl compounds, it is necessary to react at lower temperature as far as possible. If the reaction heat can not spread in time, dehydration and other reactions will occur, resulting in the formation of olefin and color. Therefore, it is necessary to select suitable agitator and adjust proper agitation speed, add P2O5 in different times, under the condition of nitrogen protection, the reaction is generally limited to 1H. At the same time, the temperature changes of the reaction system must be strictly controlled and not raised too fast.

Lan Yunjun [11,12] and others have successfully prepared PVO series phosphoric vegetable oil, PME series phosphated lanolin and phosphoric acid modified fish oil fatliquoring products by using phosphorus pentoxide twice input method and have been industrialized.

1.5 solvent addition of pentoxide pentoxide

The reaction of P2O5 with hydroxyl compounds can be carried out by means of esterification with carbon tetrachloride or benzene as solvent, followed by evaporation of solvent to obtain product [13]. Such as Tang Yongfan [1] and Zhou Fu Rong [14] have done some work in this respect. Although this method can solve the drawbacks of this heterogeneous system, these organic solvents are low and toxic, and may be volatile in the reaction process, resulting in pollution. After the reaction, all of them must be distilled and removed.

Wang Xuechuan [15] and others used alkyl sulfonyl chloride and chlorinated paraffin as composite solvent of phosphorus pentoxide, which effectively solved the problem of difficulty in adding phosphorus pentoxide. The composite solvent itself is non-toxic and volatile, so that the phosphorylation reaction is carried out in homogeneous system. The reaction is full and uniform. This compound solvent is beneficial to fatliquoring, and can be used as an effective component of leather fatliquoring agent without removing after phosphorylation. Therefore, this method is expected to be popularized.

Component analysis of 2 phosphate ester

Phosphates are usually made of mixtures of DAP, MAP, PAP and PA with different proportions. The performance of each component is very different. Therefore, component analysis of phosphate esters is needed. At present, the methods for detecting phosphate esters include 31P-NMR, TLC, HPLC, mixed indicator, potentiometric titration and conductance.

At present, chemical analysis and potentiometric titration are the main methods in China. The mixed indicator method [16] is easy to operate and convenient to calculate, and is suitable for rapid analysis in industrial production. The indicators used are: alizarin red and phenolphthalein indicator, methyl red and phenolphthalein indicator, bromine cresol green and phenolphthalein indicator three, and bromo cresol green and phenolphthalein indicator are most commonly used. Potentiometric titration, [17], uses potentiometric titrant to calculate the relative molar content of DAP, MAP and PA in phosphates by using the three distinct pH jumps in the titration process and the volume of alkali consumed during the three jump. {page_break}

Whether the composition of phosphate ester can be analyzed by potentiometric titration or mixed indicator method, the key point is the determination of third waiting points. Because the ionization constant of the three stage H+ of H3PO4 is very small (2.2 * 1013), it can not be obtained by direct titration with alkali. Indirect method must be used. Usually, calcium chloride is added to the second waiting point to transform it into insoluble calcium phosphate precipitate and free H+, then titrated by alkali solution. The data also introduce that silver nitrate solution is used instead of calcium chloride solution to turn it into insoluble silver phosphate precipitate and free hydrogen ion and then titrated [18] by alkali solution.

It is worth mentioning that after second equal points, the change of pH value is affected by the addition of calcium chloride or silver nitrate, and the soluble substance produced by adding calcium chloride or silver nitrate solution is very strong to the electrode, and the precipitation often affects the sensitivity of the electrode, thus affecting the determination of third equivalent points. Therefore, in the determination of components, the amount of CaCl2 added or the amount of silver nitrate can not be too much, but there is a minimum to ensure that the third level dissociation H+ of phosphoric acid is completely released. Generally speaking, the lowest dosage of calcium chloride or silver nitrate solution is also different for different phosphate samples, which needs to be determined by experiments.

Generally speaking, due to the influence of grease color, the mixed indicator method is difficult to determine the color of the first equivalent point, namely, the formation of blue green. However, the judgement of the color of the third equal points, namely the formation of cyanotic purple, is very accurate; and the potentiometric titration method can accurately analyze the first and second equivalent points of phosphate. Therefore, as long as the amount of CaCl2 added or the amount of silver nitrate added is more suitable, the mixed indicator method and potentiometric titration method can also cooperate with each other and verify each other.

Whether the composition of phosphate can be analyzed by potentiometric titration or mixed indicator method, it is very important to dissolve the sample and choose the appropriate solvent. Commonly used solvents are 95% ethanol, isopropanol, n-butanol, n-pentyl alcohol, acetone, isopropanol, 1,2- two chloroethane, isooctanol, toluene, benzene and other solvents. The principle of selection is to ensure that all samples are dissolved and the solution is clarified, such as potentiometric titration. Choosing proper solvent to dissolve the sample well is the necessary condition for the accurate determination of phosphate content. For different phosphate samples, different solvents or different proportions of composite solvents can be selected through experiments, so we must not blindly copy them.

3 phosphate ester fatliquoring agent

Synthetic phosphate ester fatliquors usually have long chain fatty alcohols or fatty alcohol ethers, natural oils containing hydroxyl groups or their modified oils. Long chain fatty alcohol or fatty alcohol ether as the main raw material, the phosphate ester treated leather has good elasticity, fullness, good waterproof and softness, better mercerizing effect, leather surface is not greasy, the coating layer has good adhesion with leather, and the long chain fatty alcohol is mostly C12~C18 alcohol [19-22].

In order to fully exploit the properties and fatliquoring effects of various natural oils and fats, many people have done a lot of research work. The oils and fats used include castor oil, vegetable oil, sunflower seed oil, salad oil, cottons seed oil, fish oil and lanolin. Among them, castor oil and lanolin are the most common [11,12,23-25].

Before the phosphorylation reaction, oil can be modified properly, which is more conducive to the synthesis of phosphate and the development of more excellent phosphate ester fatliquoring agents. The modification methods are mainly [26-29]: alcohol amine amine is used for amidation of animal and vegetable oils to obtain enolamides with various active groups, such as amido and hydroxyl active groups. Transesterification of animal and vegetable oils with low alcohols not only adjusts the relative mass of oils and oils, but also exposes many active groups such as hydroxyl groups. Polyethylene glycol etherification can also be used to introduce water-soluble groups such as polyoxyethylene.

In order to improve the emulsification and permeability of phosphate ester, [30-33] can also be properly treated after phosphorylation. For example, esterification reaction with HOCH2CH2N+ (CH3) 3C1- can produce amphoteric phosphate fatliquoring agent, sulfonation agent with sulfonating agent, and halogenation or sulfonation of unsaturated phosphate ester to improve flame retardancy and light fastness.

In a word, in order to better improve the superior performance of phosphate fatliquoring agent, we should design the molecule of phosphate ester from the requirement of leather industry for multifunctional and greening of fatliquoring agent, so as to make the synthesized phosphate ester have excellent comprehensive fatliquoring property. To this end, it is necessary to introduce more reactive groups or expose more reactive groups to different raw materials, so that the phosphate ester synthesized in the present stage has the best fatliquoring performance.