Dehydration acetic acid

Azeotropic Distillation. The concept of azeotropic distillation is not new. The use of benzene to dehydrate ethyl alcohol and butyl acetate to dehydrate acetic acid has been in commercial operation for many years. However, it was only during World War II that entrainers other than steam were used by the petroleum industry. Two azeotropic processes for the segregation of toluene from refinery streams were developed and placed in operation. One used methyl ethyl ketone and water as the azeo-troping agent (81) the other employed methanol (1). 

Acetic Anhydride Acetic anhydride is the most important carboxylic acid anhydride. It is produced at the rate of about 4 billion pounds per year, primarily for synthesis of plastics, fibers, and drags. (See the synthesis of aspirin on p. 1009.) Acetic anhydride consists of two molecules of acetic acid, minus a molecule of water. The most common industrial synthesis begins by dehydrating acetic acid to give ketene. 

In many cases the organic to be dehydrated (e.g., acetic acid) attacks the ether linkage in the PVA membrane. Indeed, the PVA membrane has very limited fife in the presence of most acids. Ray et al. [14] used the concept of copolymer membranes to dehydrate acetic acid over the entire range of concentration from 0% to 100%. These investigators prepared copolymers of acrylonitrile (AN) with different hydrophUic monomers like hydroxy ethyl methacrylate, acrylic acid, methacrylic acid, and itaconic acid. These copolymers have carbon-carbon bonds, which unlike the ether linkage in the cross-hnked PVA membrane are stable to the attack by carboxyhc acids. The acrylonitrile part is not sufficiently hydrophihc but imparts mechanical strength while the other monomers improve the hydrophilicity. The overall result is an efficient yet stable membrane. Variation of the ratio of AN to (the other) monomer allows freedom of adjusting the hydrophUicity of the membrane to achieve certain... 

Carbon monoxide High-pressure Off-gas Light ends Catalyst recovery Dehydration Acetic acid Acetic acid Heavy ends... 

Othmer D. R, Azeotropic distillation for dehydrating acetic acid. Chemical and Metallurgical Engineering, 91-94 (June 1941). 

To prepare pure acetic acid (glacial acetic acid), the crude aqueous product is converted into the sodium salt, the latter dehydrated by fusionf and then heated with concentrated sulphuric acid anhydrous acetic acid, b.p. 118°, distils over. Only the preparation of aqueous acetic acid and of crystalline copper acetate is described below. 

Directly from the corresponding acid and alcohol, in the presence of a dehydrating agent. Thus when ethanol and acetic acid are mixed, ethyl acetate and water are formed, but in addition an equilibrium is established. 

Dehydration of the corresponding ammonium salt. Thus ammonium acetate on heating loses water giving acetamide. An excess of acetic acid is... 

Similarly, 5-thiazole alkanoic acids and their salts are obtained from thioamides and /3-halo -y-keto acids (695). Thus thioarylamides condensed with 3-aroyl-3-bromopropionic acid (88) in isopropanolic solution in the presence of Na COs give first 4-hydroxy-2-aryl-A-2-thiazoline-5-acetic acid intermediates (89), which were dehydrated in toluene with catalytic amounts of p-toluene sulfonic acid to 2,4-diaryl-5-thiazole acetic acid (90) (Scheme 39) (657), with R = H or Me Ar = Ph, o-, m- or p-tolyl, o-, m-, or P-CIC6H4, 0-, m-, or p-MeOC(iH4, P-CF3C6H4, a-thienyl, a-naphthyl (657). 

Perchloric acid Acetic acid, acetic anhydride, alcohols, antimony compounds, azo pigments, bismuth and its alloys, methanol, carbonaceous materials, carbon tetrachloride, cellulose, dehydrating agents, diethyl ether, glycols and glycolethers, HCl, HI, hypophosphites, ketones, nitric acid, pyridine, steel, sulfoxides, sulfuric acid... 

The bottoms from the solvent recovery (or a2eotropic dehydration column) are fed to the foremns column where acetic acid, some acryflc acid, and final traces of water are removed overhead. The overhead mixture is sent to an acetic acid purification column where a technical grade of acetic acid suitable for ester manufacture is recovered as a by-product. The bottoms from the acetic acid recovery column are recycled to the reflux to the foremns column. The bottoms from the foremns column are fed to the product column where the glacial acryflc acid of commerce is taken overhead. Bottoms from the product column are stripped to recover acryflc acid values and the high boilers are burned. The principal losses of acryflc acid in this process are to the aqueous raffinate and to the aqueous layer from the dehydration column and to dimeri2ation of acryflc acid to 3-acryloxypropionic acid. If necessary, the product column bottoms stripper may include provision for a short-contact-time cracker to crack this dimer back to acryflc acid (60). 

Vapor-Phase Condensations of Acetic Acid or Esters with Formaldehyde. Addition of a methylol group to the a-carbon of acetic acid or esters, foUowed by dehydration, gives the acrylates. 

Anhydrous Acetic Acid. In the manufacture of acetic acid by direct oxidation of a petroleum-based feedstock, solvent extraction has been used to separate acetic acid [64-19-7] from the aqueous reaction Hquor containing significant quantities of formic and propionic acids. Isoamyl acetate [123-92-2] is used as solvent to extract nearly all the acetic acid, and some water, from the aqueous feed (236). The extract is then dehydrated by azeotropic distillation using isoamyl acetate as water entrainer (see DISTILLATION, AZEOTROPIC AND EXTRACTIVE). It is claimed that the extraction step in this process affords substantial savings in plant capital investment and operating cost (see Acetic acid and derivatives). A detailed description of various extraction processes is available (237). 

Water formed in the reaction as well as some undesirable by-products must be removed from the acetic acid solvent. Therefore, mother Hquor from the filter is purified in a residue still to remove heavies, and in a dehydration tower to remove water. The purified acetic acid from the bottom of the dehydration tower is recycled to the reactor. The water overhead is sent to waste treatment, and the residue still bottoms can be processed for catalyst recovery. Alternatively, some mother Hquor from the filter can be recycled directiy to the reactor. 

The use of the Hquid-phase process in acetic acid with the cobalt— manganese—bromine system as explained in the tetephthaUc acid section is also possible (149). This process has been used by Amoco Chemical to produce pyromellitic acid, and facUities remain in place to do so again in the future. As with all hquid-phase oxidations of this type, yields ate high. A separate dehydration step would be needed to yield the dianhydtide. 

Amino-4-nitrophenol. This derivative, 2-hydroxy-5-nitroani1ine (9), forms orange prisms from water. These prisms are hydrated with one water of crystallization, mp 80—90°C, and can be dehydrated over sulfuric acid to the anhydrous form, mp 143 —145°C. The compound is soluble in ethanol, diethyl ether, acetic acid, and warm benzene and slightly soluble in water. 

The acid occurs both as colorless triclinic prisms (a-form) and as monoclinic prisms ( 3-form) (8). The P-form is triboluminescent and is stable up to 137°C the a-form is stable above this temperature. Both forms dissolve in water, alcohol, diethyl ether, glacial acetic acid, anhydrous glycerol, acetone, and various aqueous mixtures of the last two solvents. Succinic acid sublimes with partial dehydration to the anhydride when heated near its melting point. 

Uses ndReactions. Linalool can be estetified to linalyl acetate by reaction with acetic anhydride. Linalyl acetate [115-95-7] has a floral-fmity odor, reminiscent of bergamot and lavender. The price of the acetate in 1995 was 14.30/kg (45). Linalool is subject to dehydration and to isomerization to nerol and geraniol during the esterification. However, if the acetic acid formed during the esterification is removed in a distillation column, the isomerization can be minimized and good yields of the acetate obtained (130). 

Under acidic conditions, dehydration to an anhydrotetracycline [20154-34-1] (8), C22H22N20y, occurs under basic ones, ring C opens to an isotetracycline [3811-31-2] (9), C22H24N20g. The anhydrotetracyclines, such as (8), appear to exhibit a mode of antibacterial action, but it is unlike that of tetracycline (24). Epimerization (23,25,26) at C-4 occurs in a variety of solvents within the pH range 2—6, particularly in acetic acid (25). A number of anions (27) facihtate this reaction. The reverse process, from 4-epitetracycline [79-85-6] C22H24N20g, to tetracycline, is promoted by chelation with ions such as calcium and magnesium (28). 

Chemical Designations - Synonyms Acetic acid, zinc salt Dicarbomethoxyzine Zinc acetate dehydrate Zinc diacetate Chemical Formula Zn(CWtf) or Zn(CWtf) tfO. 

The dehydration of the 20-semicarbazones takes place in refluxing acetic acid containing acetic anhydride, and the reaction mixture is apparently homogeneous. In any case, none of the three methods permits the survival of the sensitive 11 -hydroxyl group. 

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