Carboxylation of styrenes

Scheme 7.10 Oxidative carboxylation of styrene under homogeneous conditions.

Another product of the reaction of an olefin with the O2/ CO2 mixture in the presence of Rh is the cyclic carbonate (VII) [3]. Only few reports can be found in the literature on the direct synthesis of carbonates from olefins, dioxygen and carbon dioxide, despite the usefulness of this reaction that avoids, with respect to the reaction of epoxides with carbon dioxide, the preliminary synthesis of epoxides. We have found that the product distribution in the oxidative carboxylation of styrene depends on the O2/ CO2 ratio and on the temperature (Scheme 3). As the epoxide is one of the oxidation products of styrene, it could be the origin of styrene carbonate. We have evidence that the formation of the... 

G. Filardo, S. Gambino, G. Silvestri, A. Gennaro and E. Vianello (1984) Electro-carboxylation of styrene through homogeneous redox catalysis , J. Electroanal. Chem. 177, 303-309. 

Scheme 5.8 Nickel-catalyzed reductive carboxylation of styrenes...

Williams CM, Johnson JB, Rovis T (2008) Nickel-catalyzed carboxylation of styrenes using CO2. J Am Chem Soc 130 14936-14937... 

Fig. 6. 13 Kinetics of products formation in the oxidative carboxylation of styrene at 393 K under metal oxides catalysis. Styrene oxide is formed in a slight excess with respect to benzaldehyde with a selectivity of ca. 55-60 % with respect to styrene. Reprinted with permission from [107]. Copyright (2002) Elsevier...

Table 1.6 Products of the oxidative carboxylation" of styrene using several oxides ...

Functionalization. Copolymers do not have the abiHty to exchange ions. Such properties are imparted by chemically bonding acidic or basic functional groups to the aromatic rings of styrenic copolymers, or by modifying the carboxyl groups of the acryHc copolymers. There does not appear to be a continuous functionalization process on a commercial scale. 

Both R and MMA radicals are found to be responsible for the photoinitiation process. Chaturvedi and coworkers [54,55] introduced phenyl dimethyl sulfonium-ylide cupric chloride and chromium thiophene carboxylate as the photoinitiator of styrene and MMA. No reaction mechanism was given for these systems. 

Furthermore, photochemically induced homolytical bond cleavage can also be applied when the prepolymer itself does not contain suitable chromophoric groups [113-115]. Upon thermolysis of ACPA in the presence of styrene, a carboxyl-terminated polystyrene is formed. This styrene-based prepolymer was reacted with lead tetraacetate and irradiated with UV light yielding free radicals capable of initiating the polymerization of a second monomer (Scheme 33) [113]. 

Pastor-Sempere N., Eemandez-Garcfa J.C., Orgiles-Barcelo A.C., Pastor-Bias M.M., Martfn-Martfnez J.M., and Dillard J.G., 1998, Surface treatment of styrene-butadiene rubber with carboxylic acid, in First International Congress on Adhesion Science and Technology, W.J. van Ooij and H.R. Anderson Jr. (Eds), Utrecht, VSP, 461 94. 

The use of stoichiometric ruthenium-NHC complexes generated in situ from [Ruljd-COCKp-cymene)], an imidazohnm salt [4] or an imidizol(idin)ium-2-carboxylate [4] has been applied in the cyclopropanation of styrene 5 with ethyl diazoacetate (EDA) 6 (Scheme 5.2). No base was necessary when imidazolium-2 carboxylate were employed. The diastereoselectivity was low and the cis/trans ratio was around 50/50 (Table 5.1). Although the diastereoselectivity was moderate, the reaction was highly chemoselectivity as possible side reactions (homologation, dimerisation and metathesis) were totally or partially suppressed. 

On the other hand, Doyle et al. have developed methyl 2-oxoimidazolidine-4(carboxylate ligands, containing 2-phenylcyclopropane attached at the 1-iV-acyl site, such as the (4(5),2 (7 ),3 (7 )-HMCPIM) ligand. The resulting dirhodium complex led, for the cyclopropanation of styrene with EDA, to the corresponding cyclopropane with 68% ee and 59% yield, but with almost... 

On the other hand, other chiral dirhodium(II) tetracarboxylate catalysts based on azetidine- and aziridine-2-carboxylic acids have been prepared by Zwanenburg et al. and submitted to the cyclopropanation of styrene with... 

Scheme 6.18 Rh-catalysed cyclopropanation of styrene with sulfonamide ligands derived from aziridine- and azetidine-2-carboxylic acids.

Preparation and Reactions of S-b-MM. As mentioned in the introduction, we were interested in block copolymers of styrene and alkali metal methacrylates with overall molecular weights of about 20,000 and methacrylate contents on the order of 10 mol%. The preparation of such copolymers by the usual anionic techniques is not feasible. An alternative is to prepare block copolymers of styrene and methacrylic esters by sequential anionic polymerization, followed by a post-polymerization reaction to produce the desired block copolymers. The obvious first choice of methacrylic esters is methyl methacrylate. It is inexpensive, readily available, and its block copolymers with styrene are well-known. In fact, Brown and White have reported the preparation and hydrolyses of a series of S-b-MM copolymers of varying MM content using p-toluenesulfonic acid (TsOH) (6). The resulting methacrylic acid copolymers were easily converted to their sodium carboxylates by neutralization with sodium hydroxide. 

Scheme 22 Deconvoluting the catalytic mechanism in the hydrogen-mediated coupling of styrene to carboxylic anhydrides...

The axial alignment of Rh2(5R-MEPY)4 leads to probable structures for the carbene intermediate as shown in Figure 17.15. Approach of styrene will occur with the phenyl group pointing away from the rhodium complex, and also in a trans (anti) fashion with respect to the ester group of the carbene moiety. The 2-phenylcyclopropane-l-carboxylic ester resulting from this is indeed the 1R,2R (1R-trans) diastereomer. 

K. Yeowell O Connell, W. Pauwels, M. Seven, Z. L. Jin, M. R. Walker, S. M. Rappa-port, H. Veulemans, Comparison of Styrene-7,8-oxide Adducts Formed via Reaction with Cysteine, N-Terminal Valine and Carboxylic Acid Residues in Human, Mouse and Rat Hemoglobin , Chem.-Biol. Interact. 1997, 106, 67 - 85. 

A telechelic polystyrene containing two carboxyl groups at one end of a polymer can be used as a macromonomer in a step polymerization with a diol or diamine to yield a polyester or polyamide containing graft chains of polystyrene. The required telechelic polymer is obtained by radical polymerization of styrene in the presence of 2-mercaptosuccinic acid. 

Chlorosulfonated styrene resins and carboxyaminoacid polymers were also found to possess thromboresistant properties by Josefonwicz and coworkers [483]. Studies included investigation of the effect of spacer length between amine and carboxylic groups as well as modification of styrene/isoprene/styrene blocks with chlorosulfonyl isocyanate giving sulfamate and carboxylic functionality [484],... 

---