Dimerization salts

The oxidation step of thioureas can be reversed, as was shown by cyclic voltammetry to regenerate thiourea from anodically produced dimeric salt (in AN/BU4NCIO4, potentials vs Ag/Ag+) (Scheme 1). 

Obviously, the formation of dimer 269 is due to the negative charge at the exo methine group of 267, which is not screened by substituents, and because of this fact, the a-methine carbon atom can add to position 1 of another unreacted 2-benzopyrylium cation. Such an interaction may be called a-1 dimerization it leads to dimeric salt 268 and then to pseudobase 269. 

The pathway to chrysenes, in this case, was assumed to include the formation of dimeric salts 268. Then the intramolecular interfragment interaction takes place with the formation of the C4b—CiA bond, which leads to the already familiar intermediate 272 (Scheme 14). 

A corroboration of the key role of the intermediate cation 291 is the observation of a sharp yield increase of disproportionation products 297 and 298, compared to their direct formation from salt 280 on treatment of dimer 281 with catalytic amounts of triethylammonium perchlorate, which acts as the protonating agent generating intermediate 293. The formation of unsaturated dimers 296 is possible not only by the direct hydride transfer, followed by deprotonation of dimeric salt 294 (pathway a, Scheme 16), but also by equivalent 1,5-hydrogen transfer in the ortho-quinonoid intermediate 295 formed by deprotonation of the acidic methine group in intermediate 291 (pathway b). 

These led to matrix studies of the structure of ion pairs and triple ions, such as the thorough studies by Devlin and coworkers on matrix isolated alkali nitrate (21), chlorate (22) and perchlorate ion pairs (23 ). For relatively simple salts, such as the alkali halides, investigations were conducted into the structure of the dimeric salt species (6, 7, ), which is present in a gas phase equilibrium with the monomeric salt species. These dimers have been found to be very strongly bound in a cyclic structure. 

In addition to these compounds, a number of dimeric salts containing the di-//-hydroxy bridged species [(H20)58c(/r-0H)28c(H20)5] + ions (9) have been characterized. 

Monovalent mercury is found only in dimeric salts such as Hg2Cl2 (calomel), vhich is sparingly soluble in vater and, again correspondingly, much less toxic than HgCl2 (sublimate). 

U.v. irradiation of [(7r-Cp)Fe(CO)2(PPh2H)]PFg yields a dimeric salt which possibly has structure (30). ... 

Many monomeric heterocyclic anhydrobases can be isolated now using specific methods (44), but application of these methods to thiazole ring did not succeed however, appropriate conditions lead to the separation of a dimer, the structure of which has been established by its NMR Spectra and chemical reactivity (26). The most probable mechanism of its formation appears identical with the one previously described in the benzothiazolium series (24). A second molecule of quaternary salt A3... 

At first, the dimeric nature of the base isolated from 3-ethyl-2-methyl-4-phenylthiazolium was postulated via a chemical route. Indeed the adduct of ICH, on a similar 2-ethylidene base is a 2-isopropylthiazolium salt in the case of methylene base it is an anilinovinyl compound identified by its absorption spectrum and chemical reactivity (45-47). This dimeric structure of the molecule has been definitively established by its NMR spectrum. It is very similar to the base issued from 2.3-dimethyl-benzo thiazolium (48). It corresponds to 2-(3 -ethyl-4 -phenyl-2 -methylenethiazolinilydene)2-methyl-3-ethyl-4-phenylthiazoline (13). There is only one methyl signal (62 = 2.59), and two series of signals (63= 1.36-3.90, 63= 1.12-3.78) correspond to ethyl groups. Three protons attributed to positions T,5,5 are shifted to a lower field 5.93, 6.58, and 8.36 ppm. The bulk of the ten phenyl protons is at 7.3 ppm (Scheme 22). 

CTD.ORINE OXYGEN ACIDS AND SALTS - DICTD.ORINE MONOXIDE, HYPOCTD.OROUS ACID, AND HYPOCm ORITES] (Vol 5) Alkylketene dimers (AKD)... 

Biguanide salts Biimidazole dimer Biisobutyryl [4388-87-8] Bilarcil Bile acids... 

Single-Stack Acceptor. Simple charge-transfer salts formed from the planar acceptor TCNQ have a stacked arrangement with the TCNQ units facing each other (intermolecular distances of ca 0.3 nm (- 3). Complex salts of TCNQ such as TEA(TCNQ)2 consist of stacks of parallel TCNQ molecules, with cation sites between the stacks (17). The interatomic distance between TCNQ units is not always uniform in these salts, and formation of TCNQ dimers (as in TEA(TCNQ)2) and trimers (as in Cs2(TCNQ)Q can lead to complex crystal stmctures for the chainlike salts. 

Vinylacetylene and Ghloroprene. In the presence of cuprous salt solutions, acetylene dimerizes to vinylacetylene [689-97-4], C H. Yields of 87% monovinylacetylene, together with 10% of divinylacetylene, have been described (6). 

With two equivalents of an organomagnesium hahde, a Gtignard reagent is formed, capable of use in further syntheses (35,36). Cuprous salts cataly2e oxidative dimerization of propargyl alcohol to 2,4-hexadiyne-l,6-diol [3031-68-3] (37). 

RO—CF=CF2, are obtained by reaction with sodium salts of alcohols (26). An osone—TFE reaction is accompanied by chemiluminescence (27). Dimerization at 600°C gives perfluorocyclobutane, C Fg further heating gives hexafluoropropylene, CF2=CFCF2, and eventually perfluoroisobutylene, CF2=C(CF2)2 (28). Purity is deterrnined by both gas—Hquid and gas—soHd chromatography the in spectmm is complex and therefore of no value. 

Commercially, polymeric MDI is trimerized duting the manufacture of rigid foam to provide improved thermal stabiUty and flammabiUty performance. Numerous catalysts are known to promote the reaction. Tertiary amines and alkaU salts of carboxyUc acids are among the most effective. The common step ia all catalyzed trimerizations is the activatioa of the C=N double boad of the isocyanate group. The example (18) highlights the alkoxide assisted formation of the cycHc dimer and the importance of the subsequent iatermediates. Similar oligomerization steps have beea described previously for other catalysts (61). 

Ttinitroparaffins can be prepared from 1,1-dinitroparaffins by electrolytic nitration, ie, electrolysis in aqueous caustic sodium nitrate solution (57). Secondary nitroparaffins dimerize on electrolytic oxidation (58) for example, 2-nitropropane yields 2,3-dimethyl-2,3-dinitrobutane, as well as some 2,2-dinitropropane. Addition of sodium nitrate to the anolyte favors formation of the former. The oxidation of salts of i7k-2-nitropropane with either cationic or anionic oxidants generally gives both 2,2-dinitropropane and acetone (59) with ammonium peroxysulfate, for example, these products are formed in 53 and 14% yields, respectively. Ozone oxidation of nitroso groups gives nitro compounds 2-nitroso-2-nitropropane [5275-46-7] (propylpseudonitrole), for example, yields 2,2-dinitropropane (60). 

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