Cellulose phosphoric acid esters

The heat exchanger fins from aluminum or its alloy are coated with aqueous solution containing a water-soluble cellulose resin or polyvinyl alcohol and a surfactant to form a hydrophilic film. Phosphoric acid ester was used as anionic surfactant (0.05-4.5%) in aqueous solution to form a hydrophilic film showing contact angle with water of 5-32° [288]. 

Phosphoric acid-based systems, for cellulosics, 11 488 Phosphoric acid esters, 24 159 Phosphoric acid fuel cells (PAFC), 13 858— 860 12 203-204, 216-219 19 626 effects of carbon monoxide and sulfur in, 12 219... 

For the determination of phosphoms chemically bound to cellulose, impregnated samples were washed with water with a modulus of 1 200, then dried under reduced pressure at 40 °C. The washed sample (20-100 mg) was suspended in a potassium chloride solution (0.75 g of K.C1 in 25 ml of water), and was titrated potentiometrically with 0.025 N NaOH. The degree of substitution for phosphoric acid esters (mono-, di-and tri-esters) was determined by titration curve differentiation [17],... 

The data presented in Table 2 demonstrate that pretreatment of impregnated celluloses at 100 C does not lead to chemically bound phosphorous and formation of esters, i.e. phosphoric acid was completely washed off from cellulose. However, phosphoric acid esters as monophosphates could be detected in the impregnated cellulose samples after heating them at 160 and 200 °C,... 

The essential elements of Table 2.1 meet these demands. In all cases they are components of the metabolic system in cell or of important final products for example, cellulose for the upright standing of the plant. The function as constituents of such compounds is clear for C, H, and O. These three elements are together components of nearly all organic compounds in the plant [only hydrocarbons (e.g., carotins) are free of O], and therefore they build up the planfs shape. A similarly clear situation holds true for N and P, both of which are constituents of the information carriers DNA and RNA. N is a component of their purine and pyrimidine bases, while phosphoric acid esters of D-ribose or 2-deoxy-D-ribose form the backbone of their nucleotide sequences. Moreover, P plays a very important role in energy metabolism, the key compounds being nucleotide phosphates (e.g., adenosine triphosphate, ATP) (see Scheme 2.1) and the homologous molecules... 

Phosphorylation of microcrystalline cellulose under the action of microwave irradiation was achieved by Gospodinova et al. [83]. The reactions were performed in a single-mode microwave reactor under an argon atmosphere. Mixtures of 29.0 mmol urea, 17.6 mmol phosphorous acid, and 1.8 mmol cellulose were irradiated for 60 to 120 min at temperatures from 75 to 150 °C (Scheme 14.42). The process led to monosubstituted phosphorous acid esters of cellulose with different degrees of substitution of hydroxy functions (0.2 to 2.8) without pretreatment with solvents. 

The low-volatility, flame-resistant phosphoric acid esters have maintained their position in products subjected to high levels of mechanical strain such as conveyor belts. Triphenyl phosphate, used only for molding compounds made of cellulose esters, is a practically noncombustible product that is not soluble in benzine. Tricresyl phosphate (TCP) is a flame-retardant plasticizer for PVC products subjected to heavy mechanical stress. The esters of the aliphatic dicarboxylic acids (adipic, azelaic, and sebacic acid) are used as plasticizers for PVC and PVAC. These products are resistant to cold and light. The esters of higher fatty acids such as pelargonates, laurates, palmitates, stearates, and ricinoleates are, strictly speaking, not plasticizers, but are rather used as extenders, secondary plasticizers, or lubricants. 

Phosphoric Acid Esters. TCP, trioctyl phosphate (TOP), diphenyl 2-ethyl-hexyl phosphate, and tri(2-ethylhexyl) phosphate are used as flame retardants as well as plasticizers. They have a low volatility, resist oil extraction well, and are usually combined with other plasticizers. TCP is used with PVC and cellulose nitrate especially for electrical insulators it is not recommended for elastic materials to be used at low temperature. TOP is a better choice in this case but offers a lower resistance to kerosene and oil extraction. Diphenyl 2-ethylhexyl phosphate can be used for materials designed for low-temperature applications. 

Nearly all macromolecular natural products are combinations of smaller compounds. Molecular weights of monomeric compounds rarely exceed 600. Polysaccharides (starch, cellulose) are linke d by hemiacetal bonds proteins, by acid-amide bonds, also called peptide bonds (see Table III). Ester linkages are found in fats and lipids (not of very high molecular weights) as well as in the macro-molecular nucleic acids, which are phosphoric acid esters. 

Urea—Phosphate Type. Phosphoric acid imparts flame resistance to ceUulose (16,17), but acid degradation accompanies this process. This degradation can be minimized by iacorporation of urea [57-13-6]. Ph osph oryl a ting agents for ceUulose iaclude ammonium phosphate [7783-28-0] urea—phosphoric acid, phosphoms trichloride [7719-12-2] and oxychloride [10025-87-3] monophenyl phosphate [701-64-4] phosphoms pentoxide [1314-56-3] and the chlorides of partiaUy esterified phosphoric acids (see Cellulose esters, inorganic). 

CP esters are generally prepared as the ammonium salt [9038-38-4] by the reaction of cellulose with phosphoric acid and urea at elevated temperatures (130—150°C). The effects of temperature and urea/H PO /cellulose composition on product analysis have been investigated (33). One of the first commercially feasible dameproofing procedures for cotton fabric, the Ban-Flame process (34,35), was based on this chemistry. It consists of mixing cellulose with a mixture of 50% urea, 18% H PO, and 32% water. It is then pressed to remove excess solution, heated to 150—175°C for 5—30 minutes, and thoroughly washed (36). 

Cellulose phosphate esters are produced from reaction with phosphoric acid and urea. The products are used to treat hypercalciuria because of its ability to bind calcium. It has also been used for the treatment of kidney stones. 

Like all carbohydrates, cellulose possesses the clearly marked prominent properties of an alcohol owing to the presence of hydroxyl (alcoholic) groups. The presence of those groups explains the ability of cellulose to form esters with nitric acid and with acetic acid which have attained great practical importance, and also with sulphuric, phosphoric and different organic adds, as well as the formation of cellulose ethers. 

One of the arguments against the existence of micelles in solutions of cellulose derivatives is the fact that when cellulose is converted into its derivative, e.g. an ester, the degree of polymerization remains almost unchanged. This however only occurs when ester fonnation is carried out under strictly controlled conditions (nitration at low temperature with nitric and phosphoric acids mixture — p. 341, or with nitric, acetic acids and acetic anhydride mixtures — p. 344). The relevent data found by Staudinger and Mohr [32] are collected in Table 40. 

Phosphate esters (alkyl or aryl, or mixed) of phosphoric acid constitute an important family of organophosphorus flame retardants.25 Triethylphosphate, a colorless liquid boiling between 209°C and 218°C, and containing 17 wt % phosphorus, has been used commercially as an additive for polyester resins/laminates and in cellulosics. In polyester resins, it functions as a viscosity depressant as well as a flame retardant. Trioctylphosphate is employed as a speciality flame-retardant plasticizer for vinyl composites where low temperature flexibility is critical. It can be also included in blends, along with general purpose plasticizers, such as phthalate esters, to improve low temperature flexibility. 

Cellulose is esterified with certain inorganic acids such as nitric acid, sulfuric acid, and phosphoric acid. A prerequisite is that the acids used can bring about a strong swelling thus penetrating throughout the cellulose structure. The esterification can be considered as a typical equilibrium reaction in which an alcohol and acid react to form ester and water. Of the inorganic esters cellulose nitrate is the only important commercial product. 

Considerable interest has been directed to the preparation of cellulose phosphates because of their flame retarding properties and potential use in textiles. Phosphorylation can be accomplished in several ways, e.g., by heating cellulose at high temperatures with molten urea and phosphoric acid. Other phosphor-containing esters of cellulose include phosphites, phosphinates, and phosphonites. In addition, boric acid esters have been prepared. 

Studies of the synthesis of phosphorus-containing derivatives of cellulose fall into two groups phosphorylation of cellulose with derivatives of phosphoric acids and phosphorous acids, respectively. Until recently, most studies have been of derivatives of cellulose and phosphoric compounds. There are a few publications reporting the synthesis of esters of phosphorous acids and cellulose, but the properties of these compounds have not been studied at all. However, esters ctf phosphorous adds and cellulose can be used for the preparation ctf ters of phosphoric adds and cellulose, which cannot be obtained by direct synttesis (or only with difficulty) by the reaction of the hydroxyl groups of the cellulose macromolecule with phosphorus-containing reagents. 

The various ways in which esters of cellulose and phosphorous adds can be synthesized are esterification cellulose with free acids alcoholysis, with cellulose, of the esters and amides of phosphoric adds and esterification with mixed anhydrides df phosphoric adds and carboxylic adds. 

It is known that low-molecular-weight esters of phosphorous acid react, in the presence of alkali catalysts, with formaldehyde to give the corresponding hydroxymethyl phosphonates. This reaction was used to synthesize cellulose hydroxymethylphosphonates (V). The structure of these compounds has been confirmed by hydrolysis to hydroxymethyl-phosphonic acid, which was identified by paper chromatography. 

Effect of interaction of acid and cellulose at the stages of impregnation and thermal pretreatment depends on the cellulose properties. The celluloses under study have different ratios of ordered and amorphous regions. They differ also by their degree of polymerization (Table 1) and hydrophilic properties. The presence of phosphoric acid affects the system of the cellulose hydrogen bonds, the crystallinity index and leads to the formation of esters [11,12, 19],... 

Besides ester formation another effect of phosphoric acid is hydrolytic splitting of glycosidic bonds. This effect is more pronounced for celluloses with a higher DP and depends also on the amount of acid used for impregnation and the pretreatment temperature. 

Despite wide variations of synthesis conditions, the treatment of cellulose with dimethylphosphite, monomethylphosphite and phosphorous acid failed to yield phosphites containing only one type of phosphorus-containing groups. This difficulty was overcome by using phosphoric anhydrides as the esterifying reagents. The action of mixed anhydrides of phosphorous acids and acetic acid on cellulose has yielded cellulose esters with alkyl-(methyl-)phosphorous acid (73) ... 

Of the methods of synthesis of cellulose esters, the one that has been most thoroughly studied is the reaction of trans-esterification, and this method is widely used for the synthesis of low-molecular-weight esters. The alcoholysis of a low-molecular-weight ester (methyl- and n -propyl-borate) with hydroxyl groups of cellulose was first used (37) for die preparation of cellulose borate. This was followed by the trans-esterification, with cellulose, of the esters of phosphorous acids (see above), i.e. mono-, di- and trimethylphosphites (71, 72, 75), esters of phosphonic acids (76), and also phenyl-/ -chloroethyl- and / -fluoroethylphosphites (77, 78). Of considerable interest is the reaction of alcoholysis, with cellulose, of the esters of aryl- and naphthalenesulphonic add, which results in the formation of cellulose ethers, rather than esters (79-81). 

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