Dehydration thermal

CHa CHlCH CHO. Colourless lachrymatory liquid with a pungent odour. B.p. 104 "C. Manufactured by the thermal dehydration of aldol. May be oxidized to crotonic acid and reduced to crolonyl alcohol and 1-butanol oxidized by oxygen in the presence of VjOj to maleic anhydride. It is an intermediate in the production of l-butanol from ethanol. 

Other Syntheses. Acryhc acid and other unsaturated compounds can also be made by a number of classical elimination reactions. Acrylates have been obtained from the thermal dehydration of hydracryhc acid (3-hydroxypropanoic acid [503-66-2]) (84), from the dehydrohalogenation of 3-halopropionic acid derivatives (85), and from the reduction of dihalopropionates (2). These studies, together with the related characterization and chemical investigations, contributed significantly to the development of commercial organic chemistry. 

The main features in which the Radford process differs from the batch operation are in thermal dehydration and compounding. Water-wet nitrocellulose on a continuous vacuum belt filter is vacuum-dried followed by hot air transfusion (80°C) to reduce the moisture to less than 2%. After cooling, alcohol is sprayed on the nitrocellulose to a concentration of 15—20%. The alcohol-wet nitrocellulose is then transferred from a surge feeder to a compounder by a continuous weigh-belt along with the other ingredients of the composition, which are also weighed and added automatically. 

Polyethers are also products of commercial importance. Ethers can be formed by thermal dehydration, as shown for the formation of dipropylene glycol from propylene glycol. CycHc ethers can form by elimination of water from di- or tripropylene glycol. 

Carboxylic acid hydiazides are prepared from aqueous hydrazine and tfie carboxylic acid, ester, amide, anhydride, or halide. The reaction usually goes poody with the free acid. Esters are generally satisfactory. Acyl halides are particularly reactive, even at room temperature, and form the diacyl derivatives (22), which easily undergo thermal dehydration to 1,3,4-oxadiazoles (23). Diesters give dihydtazides (24) and polyesters such as polyacrylates yield a polyhydrazide (25). The chemistry of carboxyhc hydrazides has been reviewed (83,84). 

Maleic acid can be thermally dehydrated to maleic anhydride (69) or dehydrated through azeotropic distillation. Solvents such as xylenes (70) or dibutyl phthalate [84-74-2] (71) are preferred but conditions must be carefully adjusted to avoid isomerization to fumaric acid. 

Sodium Pyrophosphates. Known pyrophosphate compounds in the Na20—H2O—P20 system are given in Table 10. Commercially important sodium pyrophosphates include tetrasodium pyrophosphate (TSPP), Na4P20y, and disodium pyrophosphate, Na2H2P20y, commonly referred to as sodium acid pyrophosphate (SAPP). These are prepared industrially by thermal dehydration of disodium and monosodium orthophosphate, respectively. Tetrasodium pyrophosphate exists in five crystalline modifications, only one of which is stable at room temperature. 

Potassium Pyrophosphates. Tetrapotassium pyrophosphate (TKPP), is easily prepared by thermal dehydration of K HPO. TKPP... 

Calcium Pyrophosphates. As is typical of the pyrophosphate salts of multiple-charged or heavy-metal ions, the calcium pyrophosphates are extremely insoluble ia water. Calcium pyrophosphate exists ia three polymorphic modifications, each of which is metastable at room temperature. These are formed progressively upon thermal dehydration of calcium hydrogen phosphate dihydrate as shown below. Conversion temperatures indicated are those obtained from thermal analyses (22,23). The presence of impurities and actual processing conditions can change these values considerably, as is tme of commercial manufacture. 

The general manufacturing scheme for phosphate salts is shown in Figure 11. Condensed phosphates are prepared from the appropriate orthophosphate or mixture of orthophosphates, so the preparation of orthophosphates must be considered first for the manufacture of any phosphate salt. Phosphoric acid is neutralized to form a solution or slurry with a carefully adjusted acid/base ratio according to the desired orthophosphate product. The orthophosphate may be recovered either by crystallization from solution, or the entire solution or slurry may be evaporated to dryness. The dewatering (qv) method is determined by the solubihty properties of the product and by its desired physical properties such as crystal size and shape, bulk density, and surface area. Acid orthophosphate salts may be converted to condensed phosphates by thermal dehydration (calcination). 

The dimer of phosphonic acid, diphosphonic acid [36465-90-4] (pyrophosphoms acid), H4P2O3, is formed by the reaction of phosphoms trichloride and phosphonic acid in the ratio of 1 5. It is also formed by the thermal decomposition of phosphonic acid. Unlike the chemistry of phosphoric acid, thermal dehydration does not lead to polymers beyond the dimer extended dehydration leads to a disproportionation to condensed forms of phosphoric acid, such as [2466-09-3] and phosphine. 

HemimeUitic acid is not manufactured commercially but is available as a laboratory chemical in a hydrate form (99). Like ttimesic acid, it is formed when coal-like materials are oxidized, but can be synthesized in a purer form by oxidizing hemimeUitene [562-73-8] (1,2,3-trimethylbenzene) or hemimeUitol [526-85-2]. HemimeUitic anhydride can be produced by thermal dehydration of the acid in trichiorohenzene at 261°C (147). Synthesis of hemimellitic acid and anhydride have been described (148). There are no reported uses which ate unique to hemimellitic acid. 

Iron Oxide Reds. From a chemical point of view, red iron oxides are based on the stmcture of hematite, a-Fe202, and can be prepared in various shades, from orange through pure red to violet. Different shades are controlled primarily by the oxide s particle si2e, shape, and surface properties. Production. Four methods are commercially used in the preparation of iron oxide reds two-stage calcination of FeS047H2 O precipitation from an aqueous solution thermal dehydration of yellow goethite, a-FeO(OH) and oxidation of synthetic black oxide, Fe O. ... 

The final product of all the above processes is iron(III) oxide, a-Fe202, but its properties are deterrnined by the method of preparation. Thermal dehydration of goethite yields a pigment of lowest (4.5 g/cm ) density. The highest (5.2 g/cm ) density pigment is one prepared by two-stage calcination. The particle si2e varies from 0.3 to 4 p.m the refractive index varies from 2.94 to 3.22. 

CeOCl. The anhydrous cerous chloride [7790-86-5] can be made from the hydrated salt by suppressing oxyhahde formation during thermal dehydration by the presence of hydrogen chloride or ammonium chloride. The anhydrous salt is soluble in a variety of organic solvents, eg, alcohols and ethers, has mp 817°C, and can be volatilized at high temperatures in vacuum. 

The pentahydrate Bi(N03)3.5H20 can be crystallized from solutions of Bi oxide or carbonate in cone HNO3. Dilution causes the basic salt BiO(N03) to precipitate. Attempts at thermal dehydration yield complex oxocations by reactions which have been formulated as follows ... 

S-O 164.5 pm, S-O, 144 pm) they are made by thermal dehydration of MHSO4. Likewise the trisulfate ion SsOio " is known and also the penta.sulfate ion, SsO, whose structure indicates an alternation of S-O interatomic distances and very long O-S distances to the almost planar terminal SO3 groups ... 

In 1935, Wenker" first prepared P-aminoethyl sulfate ester (4, a solid) from thermal dehydration of monoethanolamine acid sulfate at 250°C according to Gabriel s procedure." Subsequently, the mixture of 4 and 40% NaOH aqueous solution was distilled. Further fractional distillation of the distillate in the presence of KOH and then Na at 55-56 C led to pure aziridine in 26.5% yield. 

The low condensation of diacyl chloride and bis-orf/zo-aminophenol gave a polyhydroxy amide that was submitted to a thermal dehydration.185 187 The two functions of an aminophenol could be acylated, and the question of chemose-lective acylation has been discussed.188 The problem is not O-acylation versus N-acylation because the N-acylated product is tire more stable isomer, but the question is how to control N-monoacylation versus diacylation that could reduce the molecular weight. It has been shown that the condensation in the presence of inorganic salt (LiCl) in NMP gives selectively the N-monoacylated... 

Lewis, T. W. Curtin, D. Y. Paul, I. C. Thermal, photochemical and photonucleated thermal dehydration of /j-hydroxytriary I methanols in the solid state. (3,5-Dimethyl-4-hydroxyphenyl)diphenyl methanol and (3,5-dibromo-4-hyrdoxyphenyl)di phenyl methanol X-ray crystallography of (4-hydroxyphenyl)diphenyl methanol and its 3,5-dimethyl derivative. J. Am. Chem. Soc. 1979, 101, 5717-5725. 

When prepared by thermal dehydration of 4-hydroxybenzenesulfonic acid, the reaction mixture begins to decompose exothermally around 240° C. Decomposition is delayed but still occurs at lower temperatures (160°C), and the presence of iron reduces the time to maximum rate of decomposition. Above 800 ppm of iron, the time to maximum rate is less than the dehydration reaction time, leading to severe control problems. Improved processing conditions were developed. 

Bloodworth, A. J., et al., J. Chem. Soc., Perkin Trans. 1, 1983, 471-473 Attempted thermal dehydration of benzeneseleninic acid, formed by oxidation of diphenyl diselenide with hydrogen peroxide, gave a solid which exploded at 53-55°C. The solid may have been the complex of the acid with hydrogen peroxide. 

Table 1 Occurrence and removal of emerging pollutants in thermally dehydrated sewage sludge after solid-phase treatment with T. versicolor... 

Since it was known that theophylline monohydrate can be thermally dehydrated to form either the stable Form I or the metastable Form I, the effect of different drying methods on the phase composition was studied [89], Using either a multichamber microscale fluid bed dryer or the hot stage of a variable-temperature XRPD diffractometer, Form I was produced when the drying was conducted at 40-50°C. Drying at 60°C in the VT-XRPD unit yielded only Form I, while mixtures of products were produced in the microscale fluid bed dryer even at temperatures as high as 90 °C. 

M. Kurszewska, E. Skorupowa, J. Madaj, A. Konitz, W. Wojnowski, and A. Wisniewski, The solvent-free thermal dehydration of hexitols on zeolites, Carbohydr. Res., 337 (2002) 1261-1268. 

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