DABCO

Allylic carbonates are most reactive. Their carbonylation proceeds under mild conditions, namely at 50 C under 1-20 atm of CO. Facile exchange of CO2 with CO takes place[239]. The carbonylation of 2,7-octadienyl methyl carbonate (379) in MeOH affords the 3,8-nonadienoate 380 as expected, but carbonylation in AcOH produces the cyclized acid 381 and the bicyclic ketones 382 and 383 by the insertion of the internal alkene into Tr-allylpalladium before CO insertion[240] (see Section 2.11). The alkylidenesuccinate 385 is prepared in good yields by the carbonylation of the allylic carbonate 384 obtained by DABCO-mediated addition of aldehydes to acrylate. The E Z ratios are different depending on the substrates[241]. 

A related compound, the peroxohydrate of melamine, C H N, was made by Peroxid-Chemie but discontinued in the 1980s. In addition, a diperoxohydrate of the organic base DABCO is recogni2ed and has been used as an oxidant in organic chemistry, but such a system has been known to explode (101). 

Strong bases, such as potassium acetate, potassium 2-ethylhexoate, or amine—epoxide combinations are the most useful trimerization catalysts. Also, some special tertiary amines, such as 2,4,6-tns(A7,A7-dimethylarninomethyl)phenol (DMT-30) (6), l,3,5-tris(3-dimethylaminopropyl)hexahydro-j -triazine (7), and ammonium salts (Dabco TMR) (8) are good trimerization catalysts. 

Hydroxy group containing tertiary amines are also used because they become incorporated into the polymer stmcture, which eliminates odor formation ia the foam (3). Delayed-action or heat-activated catalysts are of particular interest ia molded foam appHcations. These catalysts show low activity at room temperature but become active when the exotherm builds up. In addition to the phenol salt of DBU (4), benzoic acid salts of Dabco are also used (5). 

Amine catalysts for polyurethane appHcations are sold by Air Products (Dabco), Abbott (Polycat), Kao Corporation (Kaolizer), Tosoh Corporation (Toyocat), and Union Carbide (Niax). 

Hydroxy-3-methylenetrldecan-2-one (2). A solution of decanal 1 (3.12 g, 20 mmol), methyl vinyl ketone 2 (1.4 g, 20 mmol) and 1,4-diazablcyclo-octane (DABCO) (0 33 g,... 

Dinitrofluorobenzene, DABCO, DMF, 85% yield. When this group was used to protect an anomeric center of a carbohydrate, only the /3-isomer was formed, but this could be equilibrated to the a-isomer in 90% yield with K2CO3 in DMF. 

CMPI, DABCO.cljoxane, 2 h, 20°, 96% yield. co H (CMPI = 2-chloro-l-methylpyridinium iodide)... 

H2NOH-HC1, DABCO, MeOH, rt, 87% for a camphor derivative. This method was reported to be better than when pyridine was used as the solvent and base. 

B. Di-tert-butyl dicarbonate. A solution of 20.0 g. (0.076 mole) of di-i-butyl tricarbonate in 75 ml. of carbon tetrachloride is placed in a 600-ml. beaker fitted with a magnetic stirrer, and 0.10 g. (0.0009 mole) of freshly sublimed l,4-diazabicyclo[2.2.2]octane (DABCO) is added (Note 9). Rapid evolution of carbon dioxide begins at once. The reaction mixture is stirred at 25° for 45 minutes to complete the loss of carbon dioxide (Note 10), and then 35 ml. of water, containing sufficient citric acid to make the aqueous layer slightly acidic, is added. The layers are separated and the organic layer is dried over anhydrous magnesium sulfate and then concentrated at 25° with a rotary evaporator. The residual liquid is distilled under reduced pressure to separate 13.3-15.1 g. (80-91%) of di-butyl dicarbonate as a colorless liquid, b.p. 55-56° (0.15 mm.) or 62-65° (0.4 mm.) n T> 1.4071-1.4072 (Note 11). 

In recent years there has been some substitution of TDI by MDI derivatives. One-shot polyether processes became feasible with the advent of sufficiently powerful catalysts. For many years tertiary amines had been used with both polyesters and the newer polyethers. Examples included alkyl morpholines and triethylamine. Catalysts such as triethylenediamine ( Dabco ) and 4-dimethyla-minopyridine were rather more powerful but not satisfactory on their own. In the late 1950s organo-tin catalysts such as dibutyl tin dilaurate and stannous octoate were found to be powerful catalysts for the chain extension reactions. It was found that by use of varying combinations of a tin catayst with a tertiary amine... 

TsCl, DABCO, CH2CI2, MTBE or AcOEt, 45-97% yield. In many cases, these conditions were found to be superior to the use of pyridine as a base. DABCO is also less toxic than pyridine, which may prove useful in a commercial setting. 

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