Propylene allylic chlorination

If we wish to direct the attack of halogen to the alkyl portion of an alkene molecule, then, we choose conditions that are favorable for the free-radical reaction and unfavorable for the ionic reaction. Chemists of the Shell Development Company found that, at a temperature of 500-600°, a mixture of gaseous propylene and chlorine yields chiefly the substitution product, 3-chloro-l-propene, known as allyl chloride (CH2=CH—CH2— = allyl). Bromine behaves similarly. 

Derivation (1) By-product of soap manufacture (2) from propylene and chlorine to form allyl chloride, which is converted to the dichlorohydrin with hypo-chlorous acid this is then saponified to glycerol with caustic solution (3) isomerization of propylene oxide to allyl alcohol, which is reacted with peracetic acid, (the resulting glycidol is hydrolyzed to glycerol) (4) hydrogenation of carbohydrates with nickel catalyst (5) from acrolein and hydrogen peroxide. 

Example 5-2 It is proposed to design a pilot plant for the production of allyl chloride. The reactants consist of 4 moles propylene/mole chlorine and enter the reactor at 200°C. The reactor will be a vertical tube of 2 in. ID. If the combined feed rate is 0.85 lb mole/hr, determine the conversion to allyl chloride as a function of tube length. The pressure may be assumed constant and equal to 29.4 psia. 

AUyl Chloride High-temperature Chlorination of Propylene Allyl chloride is manufactured by the noncatalytic chlorination of propylene... 

Preparation of Glycerol. When propylene is chlorinated at temperatures above 200 C, yields of 85-90 per cent of allyl chloride are obtained. This can be converted to glycerol by a number of procedures, one of which is depicted below. 

The process involving ahyl alcohol has not been industrially adopted because of the high production cost of this alcohol. However, if the aUyl alcohol production cost can be markedly reduced, and also if the evaluated cost of hydrogen chloride, which is obtained as a by-product from the substitutive chlorination reaction, is cheap, then this process would have commercial potential. The high temperature propylene—chlorination process was started by Shell Chemical Corporation in 1945 as an industrial process (1). The reaction conditions are a temperature of 500°C, residence timp 2—3 s, pressure 1.5 MPa (218 psi), and an excess of propylene to chlorine. The yield of allyl chloride is 75—80% and the main by-product is dichloropropane, which is obtained as a result of addition of chlorine. Other by-products include monochloropropenes, dichloropropenes, 1,5-hexadiene. At low temperatures, the amount of... 

Propylene oxide, made by reacting propylene with chlorine to form propylene chloro-hydrin which is then dehydrochlorinated with caustic soda or lime (Eqs. 3-5), is used in the production of polyether polyols used for producing urethane foam. It also finds use in propylene glycol for making unsaturated polyester resins and in the pharmaceutical and food industries. Epichlorohydrin (EPI), formed by chlorination of propylene to allyl chloride and then dehydrochlorination (Eqs. 6 and 7), is used to make epoxy resins for producing laminates, fiber-reinforced composites, protective coatings, and adhesives. 

Epichlorohydrin, or 3-chloro-1,2-epoxy propane (bp 115°C), is more commonly prepared from propylene by chlorination to allyl chloride, followed by treatment with hypochlorous acid. This yields glycerol dichlorohydrin, which is dehy-drochlorinated by sodium hydroxide or calcium hydroxide (9). 

A mixture of propylene and chlorine (4 1 molar) is heated at about 500°C and 2 atmospheres. Under these conditions a free radical substitution reaction occurs rather than addition at the double bond and allyl chloride is the main product. The allyl chloride may be converted to glycerol in one of two ways, namely ... 

Epichlorohydrin is made by a three-step process. First, propylene is chlorinated to form allyl chloride, which is then reacted with hypochlorous acid to give glycerol dichlorohydrin. Caustic treatment of glycerol dichlorohydrin then produces epichlorohydrin. 

Reaction Mechanism. High temperature vapor-phase chlorination of propylene [115-07-17 is a free-radical mechanism in which substitution of an allyhc hydrogen is favored over addition of chlorine to the double bond. Abstraction of allyhc hydrogen is especially favored since the allyl radical intermediate is stabilized by resonance between two symmetrical stmctures, both of which lead to allyl chloride. 

The production of allyl chloride could be effected by direct chlorination of propylene at high temperatures (approximately 500°C and one atmosphere). The reaction substitutes an allylic hydrogen with a chlorine atom. Hydrogen chloride is a by-product from this reaction ... 

Although not in the top 50, it is an important monomer for making epoxy adhesives as well as glycerine (HO-CH2-CHOH-CH2-OH). Propylene is first chlorinated free radically at the allyl position at 500°C to give allyl chloride, which undergoes chlorohydrin chemistry as discussed previously to give epichlorohydrin. The student should review the mechanism of allyl free radical substitution from a basic organic chemistry course and also work out the mechanism for this example of a chlorohydrin reaction. 

Hydrolysis of Chlorinated Hydrocarbons. The production of oxygenated aliphatics by the hydrolysis of chlorinated hydrocarbons includes the synthetic glycerol process and the amyl alcohols process. Glycerol (7) is made from propylene via allyl chloride (CH2 CHCH2C1), and competes with glycerol made from fats and oils for use in dynamite and alkyd resins, as a tobacco humectant and cellophane plasticizer, in cosmetics and pharmaceuticals, and for other applications. Amyl alcohols have been made since 1926 by the alkali hydrolysis of a mixture of amyl chlorides, made by the chlorination of pentanes from natural gasoline. Production from this source far exceeds the supply from the fusel oil by-product of fermentation processes. Amyl alcohol and its derivatives are used mainly as solvents. 

Commerciol Dichlorohydrin consists of the above two isomers, the proportions of which depend on method of prepn d 1.36-1.39, bp 175-80°, flash p 74°, Glycerol was the main source for the prepn of glycerol chloro-hydrins until the process for direct substitutive chlorination of propylene to allyl chloride paved the way for synthesis by chlorohydrination of allyl chloride. In the synthesis from glycerol, excess HCI is used in the presence of 4% acetic acid. The reaction is run at 130° to yield 90% of product which is mainly the a,y-form. Synthesis from propylene yields a mixt of approx 70% a,/8-form 8c 30% a,y-form. Addn of HCI to epichlorohydrin, CH2 CHCH> Cl, at... 

The selectivity greatly depends on the reaction temperature. Propylene,153 for example, gives allyl chloride in 25% yield at 210°C, whereas the yield is 96% at 400°C. This is explained by the reversibility of radical addition of chlorine to the double bond at high temperature, in contrast to radical substitution, which is not an equilibrium process.156... 

Allyl Chloride. The manufacture of allyl chloride, commercialized in 1945, was the first of several modem high-temperature chlorination technologies applied for hydrocarbons. Preheated dry propylene mixed with dry chlorine in a ratio of 4 1 is reacted at 500-510°C to produce allyl chloride.193-195 Chlorine reacts quantitatively in a few seconds. The main byproducts are isomeric monochloropropenes and dichloropropenes. Allyl chloride is used mainly in the manufacture of allyl alcohol and glycerol via epichlorohydrin. 

A variety of processes for synthesizing glycerol from propylene are shown in Figure 1. The first glycerol process, put on stream in 1948, followed the discovery that propylene could be chlorinated in high yields to allyl chloride [107-05-1] (see Cm.OROCARBONS AND chlorohydrocarbons, allylchloride). 

This derivative, abbreviated AC, is a transparent, mobile, and irritative liquid. It can be easily synthesized from allyl alcohol and hydrogen chloride. However, it is industrially produced by chlorination of propylene at high temperature,... 

Allyl Chloride (3-chioropropene-1). [CAS 107-05-1]. Ally I chloride can be synthesized by reaction of allyl alcohol with HCI or by treatment of allyl formate with HCI in the presence of a catalyst (ZnCLV Commercial production is by chlorination of propylene at high temperatures, about 500°C. using a large excess of propylene. It is used in the synthesis of... 

The principal kinds of thermoplastic resins include (1) acrylonitrile-butadiene-styrene (ABS) resins (2) acetals (3) acrylics (4) cellulosics (5) chlorinated polyelliers (6) fluorocarbons, sucli as polytelra-fluorclliy lene (TFE), polychlorotrifluoroethylene (CTFE), and fluorinated ethylene propylene (FEP) (7) nylons (polyamides) (8) polycarbonates (9) poly elliylenes (including copolymers) (10) polypropylene (including copolymers) ( ll) polystyrenes and (12) vinyls (polyvinyl chloride). The principal kinds of thermosetting resins include (1) alkyds (2) allylics (3) die aminos (melamine and urea) (4) epoxies (5) phenolics (6) polyesters (7) silicones and (8) urethanes,... 

To illustrate the use of the algorithm, a case of allyl chloride manufacturing was used. Allyl chloride is manufactured by means of non-catalytic chlorination of propylene. Consider the following reaction system. 

All this was later put on a sound basis as a result of more precise measurements of rate constants and of activation energies. However, it did not require precise measurements to predict which chlorinated hydrocarbons would decompose by a radical chain mechanism and which by the unimolecular mechanism. Clearly, if the chlorinated hydrocarbon, or the product from the pyrolysis of the chlorinated hydrocarbon reacted with chlorine atoms to break the chain then the chain mechanism would not exist. Such chlorinated hydrocarbons would decompose by the unimolecular mechanism. Mono-chlorinated derivatives of propane, butane, cyclohexane, etc. would afford propylene, butenes, cyclohexene, etc. All these olefins are inhibitors of chlorine radical chain reactions because of the attack of chlorine atoms at their allylic positions to give the corresponding stabilized allylic radicals which do not carry the chain. 

The key reaction in this manufacturing process is the hot chlorination of propylene, which fairly selectively gives substitution to methyl group rather than the addition to the double bond. In this chlorination step, fresh propylene is first mixed with recycle propylene. This mixture is dried over a desiccant, heated to 650-700°F, and then mixed with chlorine (C3H6 to Cl2 ratio is 4 1) and fed to a simple steel tube adiabatic reactor. The effluent gases (950°F) are cooled quickly to 120°F and fractionated. The yield of allyl chloride is 80-85 percent. 

The direct oxidation of propylene on silver catalysts has been intensively investigated, but has failed to provide results with commercial potential. Selectivities are generally too low and the isolation of propylene oxide is complicated by the presence of many by-products. The best reported selectivities are in the range 50-60% for less than 9% propylene conversion. The relatively low selectivity arises from the high temperature necessary for the silver catalysts, the radical nature of molecular oxygen, as well as the allylic hydrogens in propylene. Thus alternative routes have been studied based on the use of oxidants able to act heterolytically under mild conditions. Hypochlorous acid (chlorine+water) and organic hydroperoxides fulfill these requirements and their use has led to the introduction of the chlorohydrin (Box 2) and the hydroperoxide processes, both currently employed commercially. 

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