Basic Organic Products. Chapter 3

Chapter 3 Basic Organic Products The substances involved in the manufacture of complex organic compounds are divided into: ✔ The raw materials - Obtained by chemical processing of gaseous, liquid and solid fuels. These includes methane, ethylene, propylene, butylenes, acetylene, benzene, toluene and other individual HCs are the most important substances used for organic synthesis. ✔ The intermediate products- Obtained by processing of the initial raw materials and they are themselves used in making more valuable complex organic products. Examples. ethylene oxide, acetaldehyde, phenol, nitrobenzene and many others. ✔ The end products - plastics, fiber, dyes, pharmaceuticals etc. 1 Manufacture of Methanol and Isopropanol • Methanol was originally produced by the destructive distillation of wood (wood alcohol) for charcoal production. Currently, it is mainly produced from synthesis gas. As a chemical compound, methanol is: • highly polar, and form hydrogen bonding (has relatively high bpt (65°C), high heat of vaporization, and low volatility. • Due to the high oxygen content of methanol, it is being considered as a gasoline blending compound to reduce carbon monoxide and hydrocarbon emissions in automobile exhaust gases. 2 Cont’d… Methanol synthesis over the heterogeneous catalyst can occur by a successive hydrogenation of chemisorbed CO. 3 Uses of Methanol Methanol has many important uses as a chemical, a fuel, and a building block. • As a methylating agent - used with many organic acids to produce the methyl esters such as methyl acrylate, methylmethacrylate, methyl acetate, and methyl terephthalate. • Methanol is also used to produce dimethyl carbonate and methyl-t-butyl ether, which are an important gasoline additives (gasoline booster). 4 Major chemicals based on methanol Formaldehyde • The main industrial route for producing formaldehyde is the catalyzed air oxidation of methanol. • A silver-gauze catalyst is used in some older processes (operate at higher T0 (~ 500°C). • New processes use an iron-molybdenum oxide catalyst. Chromium or cobalt oxides are sometimes used to dope the catalyst. The oxidation reaction is exothermic and occurs at ~ 400–425°C and atmospheric pressure. 5 Uses of Formaldehyde • Formaldehyde is the simplest and most reactive aldehyde. • Condensation polymerization of formaldehyde with phenol, urea, or melamine produces phenol-formaldehyde, urea formaldehyde, and melamine formaldehyde resins, respectively. These are important glues used in producing particle board and plywood. • Condensation of formaldehyde with acetaldehyde in presence of a strong alkali produces pentaerythritol, (a polyhydric alcohol) for alkyd resin production: 6 Cont’d… 7 Manufacture of Acetaldehyde (CH3CHO) Currently, CH3CHO is obtained from ethylene by using a homogeneous catalyst (Wacker catalyst). The catalyst allows the reaction to occur at much lower T0 ( at 130°C) than those used for the oxidation or the dehydrogenation of ethanol (~500 °C). 8 Acetic Acid (CH3COOH) • The carbonylation of methanol is currently one of the major routes for acetic acid production. The basic liquid-phase process uses a cobalt catalyst at 250°C and a high pressure of 70 atm. • The newer process (Monsanto process) uses a Rhodium complex catalyst in presence of CH3I, which acts as a promoter. The reaction occurs at 150°C and atmospheric pressure. Has 99% selectivity of the catalyst. 9 Cont’d… • The key reaction in the Monsanto process: 1st step: facial oxidative addition of methyl iodide to the square planar rhodium(I) metal centre to form the octahedral rhodium(III) species. 2nd step: Carbon monoxide insertion into the cis CH3-Rh bond yields a five-coordinated acyl intermediate, 3rd step: the intermediate formed undergoes addition of carbon monoxide , 4th step : reductive elimination of the acetyl iodide to yield the original rhodium(I) complex. 10 Cont’d… ▪ Hydrolysis of the acetyl iodide by water in the aqueous-methanol feed gives acetic acid and HI, the latter reacts with methanol to regenerate methyl iodide and the cycle repeats itself. 11 Uses of Acetic Acid • The main use of acetic acid is to produce vinyl acetate (44%), followed by acetic acid esters (13%) and acetic anhydride (12%). • Vinyl acetate is used for the production of adhesives, film, paper and textiles. • Acetic acid is also used to produce pharmaceuticals, dyes, and insecticides. • Chloroacetic acid (from acetic acid) is a reactive intermediate used to manufacture many chemicals such as glycine and carboxymethyl cellulose. 12 Manufacture of Isopropanol • The production of isopropanol from propylene occurs by either a direct hydration reaction (the newer method) or by sulfation reaction followed by hydrolysis (the older process). • In the direct hydration method, the reaction occurs either in a liquid or in a vapor-phase process. • In the liquid-phase process, high pressures (80–100 atm.) and a sulfonated polystyrene cation exchange resin catalyst is used at 150°C. • An isopropanol yield of 93.5% can be realized at 75% propylene conversion. 13 Cont’d… • Gas phase hydration is carried out at 200°C and ~ 25 atm and this process employs WO3 on a silica carrier as catalyst. • Older process (sulfation route) carried out in the presence of H2SO4, but the selectivity is a little lower than the modern vapor-phase processes. • The reaction can be carried out also in mild condition and has greater possibility to form an isopropyl carbocation (a 2 0 carbonium ion) than a 10 ethyl carbonium ion. 14 synthetic uses of isopropanol: To produce esters of many acids ( such as isopropyl acetate), solvent for alkaloids, essential oils, and cellulose derivatives, myristic & oleic acids (which are used in lipsticks and lubricants) and as an emulsifier for cosmetic materials (i.e. Isopropylpalmitate). 15 Acetone Production • Acetone is produced from isopropanol by a dehydrogenation, oxidation, or a combined oxidation dehydrogenation route. a) The dehydrogenation reaction is carried out using either copper or zinc oxide catalyst at ~ 450–550°C, 95% yield is obtained b) Direct oxidation of Isopropanol with oxygen is a non-catalytic reaction occurring at ~ 90–140°C and 15–20 atm. At 15% isopropanol conversion, the ~ yield of acetone is 93% and that of H2O2 is 87%: 16 Cont’d… • Acetone can also be coproduced with allyl alcohol in the reaction of acrolein with isopropanol. • The reaction is catalyzed with MgO and ZnO catalyst combination at ~ 400°C and 1 atm. • It appears that the hydrogen produced from the dehydrogenation of isopropanol is adsorbed on the catalyst surface selectively hydrogenates the carbonyl group of acrolein. ⇒ Nowadays, most acetone is obtained via a cumene hydroperoxide process where it is coproduced with phenol. 17 Phenol and Acetone from Cumene ⇒ Phenol is produced from cumene by a two-step process. 1st step, cumene is oxidized with air to cumene hydroperoxide. The reaction conditions are ~ 100–130°C and 2–3 atm in the presence of a metal salt catalyst, 2nd step, the hydroperoxide is decomposed into phenol and acetone in the presence of an acid . The reaction conditions are ~ 80°C and slightly below atmospheric Cumene is oxidized in the liquid-phase & its oxidation product is concentrated to 80% by vacuum distillation. thus, Cumene processes are currently the major source for phenol and co-product acetone 18 Synthetic uses of acetone • Acetone is miscible with water, alcohols, and many hydrocarbons. For this reason, it is a highly desirable solvent for paints, lacquers, and cellulose acetate. • Among the important chemicals based on acetone are methylisobutyl ketone, methyl methacrylate, ketene, and diacetone alcohol. 19 Synthetic Uses of Phenol 20 ✔ Dehydrogenation of ethylbenzene to styrene occurs over a wide variety of metal oxide catalysts (Fe, Cr, Si, Co, Zn, or their mixtures ). ✔ Typical reaction conditions for the vapor-phase process are 600–700°C, at or below atmospheric pressure. ✔ ~ 90% styrene yield is obtained at 30–40% conversion 21 Cont’d… • Alternative routes for producing styrene is to dimerize butadiene to 4-vinyl-1-cyclohexene, followed by catalytic dehydrogenation to styrene • The process involves cyclo-dimerization of butadiene over a copper-loaded zeolite catalyst at 100°C and 250 psig. • To increase the yield, the cyclo-dimerization step takes place in a liquid phase process over the catalyst. • Selectivity for vinylcyclohexene (VCH) is over 99%. • In 2nd step VCH is oxidized with oxygen over an oxide catalyst in presence of steam. Conversion over 90% and selectivity to styrene of 92% can be achieved. 22 Cont’d…. • Another approach is the oxidative coupling of toluene to stilbene followed by disproportionation to styrene and benzene : 23