Acrylate formation

Detailed theoretical studies have been conducted by Papai et al. on acrylate formation mechanism via Mo- [93] and Ni-assisted [94] C-C coupling between C02... 

The thermally induced cyclopropanation of alkenes with silyldiazoacetates is virtually unknown. Silylated diazo esters are thermally rather stable and do not readily decompose to give a carbene under standard laboratory conditions. The only known cyclopropanation of this type, i.e. synthesis of 2 from ethyl diazo(trimethylsilyl)acetate and ethyl acrylate (formation of E- and Z-isomers, no yield given), probably occurs via a pyrazoline intermediate. 

A polyurethane (x)/poly(methyl methacrylate) (1) system in which the methyl methacrylate was polymerized at various intervals after the gelation of the polyurethane was studied by Allen and coworkers (4). They found that for polymerizations at 50°C, increasing the postgelation time prior to acrylic formation decreased the size of the spherical poly(methyl methacrylate) particles that formed in the polyurethane matrix but had little effect on the shear moduli. 

Scheme 5.6 Proposed mechanism for methyl acrylate formation from [(L-L)Pd(COOMe)] O3SCF3 (L-L=bpy, dppe, 2-(2-diphenylphosphino)ethylpyridine) and ethane (adapted from [38])...

Galindo A, Pastor A, Perez PJ, Carmona E (1993) Bis(ethylene)complexes of molybdenum and tungsten and their reactivity towards CO2. New examples of acrylate formation by coupling of ethylene and carbon dioxide. Organometallics 12 4443 1451... 

Schubert G, Papai I (2003) Acrylate formation via metal-assisted C-C coupling between CO2 and C2H4 reaction mechanism as revealed from density functional calculations. J Am Chem Soc 125 14847-14858... 

Bemskoetter WH, Tyler BT (2011) Kinetics and mechanism of molybdenum-mediated acrylate formation from carbon dioxide and ethylene. Organometallics 30 520-527... 

Brookhart and coworkers investigated the copolymerization of MA and ethene with 2,6-di-tso-propyl-substituted a-diimine palladium catalysts 3 (Figure 4, Section 3.24.4). Upon activation of (N N)PdMeCl precursors with sodirrm salts of noncoordinating counter ions in presence of acrylates formation of an insertion product is observed. This stmcture is exceptionally stable and can act as a preformed active catalytic species (SCC Section 3.24.4.3.2). Additionally, copolymerization of ethene with acrylates is possible as well. It could be shown by simultaneous refractive index and UV detection GPC that acrylate is uniformly incorporated in the copolymer. and NMR spectroscopies showed that the polymer is a highly branched copolymer, similar to the ethene homopolymers accessible with the same catalyst rmder similar conditions. The acrylate units are incorporated predominantly on the end of the branches. Only a small part of the resrdting ester units, proportional to the ethene pressme, is incorporated directly in the polymer backbone (Scheme 24). 

Resin and Polymer Solvent. Dimethylacetamide is an exceUent solvent for synthetic and natural resins. It readily dissolves vinyl polymers, acrylates, ceUulose derivatives, styrene polymers, and linear polyesters. Because of its high polarity, DMAC has been found particularly useful as a solvent for polyacrylonitrile, its copolymers, and interpolymers. Copolymers containing at least 85% acrylonitrile dissolve ia DMAC to form solutions suitable for the production of films and yams (9). DMAC is reportedly an exceUent solvent for the copolymers of acrylonitrile and vinyl formate (10), vinylpyridine (11), or aUyl glycidyl ether (12). 

Important side reactions are the formation of ether and addition of alcohol to the acrylate to give 3-alkoxypropionates. In addition to high raw material costs, this route is unattractive because of large amounts of sulfuric acid—ammonium sulfate wastes. 

Transesterification of a lower acrylate ester and a higher alcohol (102,103) can be performed using a variety of catalysts and conditions chosen to provide acceptable reaction rates and to minimize by-product formation and polymerization. 

Acryhc acid and esters are stabilized with minimum amounts of inhibitors consistent with stabihty and safety. The acryhc monomers must be stable and there should be no polymer formation for prolonged periods with normal storage and shipping (4,106). The monomethyl ether of hydroquinone (MEHQ) is frequentiy used as inhibitor and low inhibitor grades of the acrylate monomers are available for bulk handling. MEHQ at 10—15 ppm is generally... 

Dimer formation, which is favored by increasing temperature, generally does not reduce the quaHty of acryhc acid for most applications. The term dimer includes higher oligomers formed by further addition reactions and present in low concentrations relative to the amount of dimer (3-acryloxypropionic acid). Glacial acrylic acid should be stored at 16—29°C to maintain high quaHty. 

Table 7. Relative Ease of Copolymer Formation for 1 1 Ratios of Acrylic and Other Monomers...

Despite numerous efforts, there is no generally accepted theory explaining the causes of stereoregulation in acryflc and methacryflc anionic polymerizations. Complex formation with the cation of the initiator (146) and enoflzation of the active chain end are among the more popular hypotheses (147). Unlike free-radical polymerizations, copolymerizations between acrylates and methacrylates are not observed in anionic polymerizations however, good copolymerizations within each class are reported (148). 

Reaction conditions depend on the reactants and usually involve acid or base catalysis. Examples of X include sulfate, acid sulfate, alkane- or arenesulfonate, chloride, bromide, hydroxyl, alkoxide, perchlorate, etc. RX can also be an alkyl orthoformate or alkyl carboxylate. The reaction of cycHc alkylating agents, eg, epoxides and a2iridines, with sodium or potassium salts of alkyl hydroperoxides also promotes formation of dialkyl peroxides (44,66). Olefinic alkylating agents include acycHc and cycHc olefinic hydrocarbons, vinyl and isopropenyl ethers, enamines, A[-vinylamides, vinyl sulfonates, divinyl sulfone, and a, P-unsaturated compounds, eg, methyl acrylate, mesityl oxide, acrylamide, and acrylonitrile (44,66). 

Studies of the particle—epoxy interface and particle composition have been helphil in understanding the mbber-particle formation in epoxy resins (306). Based on extensive dynamic mechanical studies of epoxy resin cure, a mechanism was proposed for the development of a heterophase morphology in mbber-modifted epoxy resins (307). Other functionalized mbbers, such as amine-terminated butadiene—acrylonitrile copolymers (308) and -butyl acrylate—acryhc acid copolymers (309), have been used for toughening epoxy resins. 

X-Ray Diffraction. Because of the rapid advancement of computer technology (qv), this technique has become almost routine and the stmctures of moderately complex molecules can be estabUshed sometimes in as Htde as 24 hours. An example illustrating the method is offered by Reference 24. The reaction of the acrylate (20) with phenyldiazo derivatives results in the formation of pyrazoline (21). The stereochemistry of the substituents and the conformation of the ring can only be estabUshed by single crystal x-ray diffraction. 

Exposure Limits. The Occupational Safety and Health Act (OSHA) of 1990 Hsts a multitude of acetates, phthalates, formates, and acrylates along with the corresponding permissible exposure limits and threshold limit values (76). The PEL data is Hsted in Table 2. If there is potential for exposure to an organic ester for which PEL or TLV data has been identified, then an exposure limit lower than that Hsted is usually selected for working in that environment. 

The Michael-type addition of maleic hydrazide and other pyridazinones to activated alkenes, such as methyl acrylate, acrylonitrile, methyl vinyl ketone and other a,/3-unsatu-rated carbonyl compounds, results in the formation of mono-lV-substituted products. 

Yields of the primary alkyl acrylates vary somewhat, owing to occasional losses through formation of polymer, but are usually in the range of 85-99%. Some secondary alcohols react very slowly, others readily. The method has been applied to more than fifty alcohols, some of which (with percentage yields) are listed below ethyl, 99% isopropyl, 37% -amyl, 87% isoamyl, 95% -hexyl, 99% 4-methyl-2-pentyl, 95% 2-ethylhexyl, 95% capryl, 80% lauryl, 92% myristyl, 90% allyl, 70% fur-furyl, 86% citronellyl, 91% cyclohexyl, 93% benzyl, 81% (3-ethoxyethyl, 99% /S-(/3-phenoxyethoxy) ethyl (from diethylene glycol monophenyl ether), 88%. 

Peebles, L. H., Carbon fibers from acrylic precursors. In Carbon Fibers Formation, Structure, and Properties. CRC Press, Boca Raton, FL, 1995, pp. 7 26. 

Minimize stocks and segregate from other chemicals and work areas. Where appropriate, keep samples dilute or damp and avoid formation of large crystals when practicable. Add stabilizers if possible, e.g. to vinyl monomers. Store in specially-designed, well-labelled containers in No Smoking areas, preferably in several small containers rather than one large container. Where relevant, store in dark and under chilled conditions, except where this causes pure material to separate from stabilizer (e.g. acrylic acid). 

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