Acrylic acid dimer

Figure 22. Spectra in the gas phase at 323 K of hydrogenated (right part) and deuterated (left part) of acrylic acid dimer. Grayed Experimental line shape according to ref. [99]. Thick line Theoretical line shape according to Eq. (279).

O11 storage or at elevated temperatures, acrylic acid dimerizes to give 3-acryioxypropionic acid [24615-84-7] C H 04. 

In order to perform the simulation, components and die physical property package must be specified. The main con nents of this process are water, air, propylene, acrolein, acrylic acid, acetic acid, and acrylic acid dimer. The Peng-Robinson method could be used for example. 

The oxidation proceeds by the two-step catalytic process indicated above, without the isolation of the intermediate acrolein. Acrylic acid, obtained in high yield based on propylene, is isolated as an aqueous solution and purified by extraction and distillation. The principal impurities in the commercial monomer, termed glacial acrylic acid, that may affect subsequent polymerization reactions include acetaldehyde, acrolein, furfural, benzaldehyde, and acrylic acid dimer, 3-acryloxypropionic acid. Since these impurities are inhibitory in polymerization. 

For accurate and reproducible polymerization studies involving acrylic acid, distillation of the monomer is mandatory. Unlike methacrylic acid, acrylic acid dimerizes spontaneously around 30°C at a rate of 1.0-1.5% per month [Eq. (1)] [1]. 

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. 

Water-soluble polymers obtained through a radical polymerization [e.g., poly(acrylic acid) PAA] often contain sodium sulfate Na2S04 as a decomposition product of the initiator. The peak of Na2S04 is eluted before the dimer. In the interpretation of the chromatogram, a typical GPC program has to be truncated before the Na2S04 peak, or at a Mpaa value of about 200. The calibration curve in this region can be flattened by an additive small pore column as well, but the principle problem remains unsolved. 

On the other hand, a good correlation was established between auto-acceleration and the type of molecular association involving the monomer in the system. Pure acrylic acid associates by hydrogen bonds to form "cyclic dimers" and "linear oligomers". The two species are in equilibrium. 

The relative abundance of each of these species can be followed for instance by infrared analysis (4, 5). Figure 3 shows the I.R. spectrum of acrylic acid in the 17 O O cm l region. The main peak at 1705 cm-1 is due to the vibration of the carbonyl group in the cyclodimeric form, whereas the shoulders at 1730 and 1740 cm-l correspond to "open dimers" and "linear oligomers". 

Figure 4. Ratios of optical densities at 1730 cm1 (linear oligomers)/1705 cm"1 (cyclic dimers) as a function of mole fraction of acrylic acid in various solvents (1) dioxane (2) methanol (3) acetic acid (4) chloroform (5) toluene (6) CClk (4).

A variety of substrates have been catalytically hydrogenated at room temperature and 1 -atm. hydrogen pressure by pentacyanocobaltate(ll) anion. Conjugation is required for the reduction of C=C bonds The effects of detailed molecular structure on reducibility and of cyanide-cobalt ratio on mode of reduction have been noted Poisoning and reactivation of the catalyst as well as the effect of alkali are described, and mechanisms are tentatively proposed for these phenomena It is concluded that the aging reaction of pentacyanocobaltate(ll) is reversible A dimerization of acrylic acids at elevated temperatures was found ... 

The reduction of acrylic acid was attempted at elevated temperatures. Surprisingly, the reaction was found to yield not only propionic acid, but also the dimer, a-methylglutaric acid. When the reaction was conducted in the absence of hydrogen, the product obtained was 3-methylglutaconic acid, which apparently is the precursor of the saturated dimer formed in a hydrogen atmosphere. Similarly, methacrylic acid yielded a-methylene-y,y-dimethylglutaric acid when heated with cyanocobaltate (II) in the absence of hydrogen. Its structure was established via ozonolysis. Similar dimerizations have been reported for acrylic acid (I, 14), methacrylate ester (7, 11), crotonic acid (13), and its diethylamide (15). 

Toxic heavy metals, such as cadmium, lead, and mercury, are sulfur seekers that bind strongly with thiol groups, which is one of the ways in which they interact adversely with biomolecules, including some enzymes. Advantage has been taken of this tendency to use thiols in chelation therapy in heavy metal poisoning. Among the thiols tested for this purpose are meso-2,3-dimer-captosuccinic acid, diethyldimercapto succinate, a-mercapto-P-(2-furyl), and a-mercapto-P-(2-thienyl) acrylic acid.3 The structural formulas for the first two are... 

The dimerization of acrylonitrile is a cheaper route to the synthesis of highly valuable hexamethylenediamine, which is one component of the starting materials for nylon-6,6 [ 16,35] In some cases of the dimerizations of acrylic acid... 

Chapiro and Dulieu have established the dominant role of macromolecular associations from the reasons for the effects described [63]. Acrylic acid associates by hydrogen bonds, yielding a cyclic dimer or an oligomer... 

Solvents such as water, methanol, dioxan etc. stabilize the oligomeric associate. Hydrocarbons and their chlorinated derivatives do not associate with acrylic acid, and they shift equilibrium (28) to the left. The polymerization of an equilibrium mixture of oligomers and dimers in polar complexing solvents is almost 20 times more rapid than the polymerization of dimers only [64], Moreover, even with polymerization in bulk, it proceeds autocatalytically under these conditions. Oligomeric aggregates associate by hydrogen bonds on to the polymer matrix which is formed immediately after the start of the... 

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