HMDS

The United States accounts for about a third of the world s consumption of cyclohexane, or 3.785 x 10 m /yr (about 1 biUion gallons per year). U.S. producers and their 1990 capacities are Hsted in Table 13. Texaco has aimounced that it is leaving the cyclohexane business, but the timing is not yet certain. Over 90% of all cyclohexane goes to the production of nylon through either adipic acid (qv) or caprolactam (qv). The balance is used to produce 1,6-hexamethylenediamine [124-09-4] (HMD A) and for various solvent uses (see Diamines and higher amines, aliphatic Polyamides). 

Fig. 6. Schematic of hexamethylene diamine phosgenation process A, HMD A tanks B, phosgene solution tanks C, phosgenation reactor D, secondary...

PACM = bis(p-aminocyclohexyl)methane CBMA = ]>cyclohexanebis(methylamine) CBEA = p-cyclohexanebis(ethylamine) HMD = hexamethylenediamine MDA = 4, 4-methylenedianiline(bis(]>aminophenyl)methane) PXD = p-xylylenediamine. 

HMD was originally produced by Du Pont as a coproduct in the manufacture of Qiana fiber. Du Pont subsequently sold the product to Bayer. In the 1990s MDA is hydrogenated by Air Products for Bayer (see Amines, aromatic-methylenedianiline). Commercial HMDI is a mixture of three stereoisomers. Semicommercial aUphatic diisocyanates include /n j -cyclohexane-l,4-diisocyanate (CHDI) and y -tetramethylxylylene diisocyanate (TMXDI). A coproduct in the production of TMXDI is y -isopropenyl-a,a-dimethylben2yl isocyanate (TMI), which can be copolymerized with other olefins to give aUphatic polyisocyanates. 

Me3Si)2NH, Me3SiCl, Pyr, 20°, 5 min, 100% yield. ROH is a carbohydrate. Hexamethyldisilazane (HMDS) is one of the most common sily-lating agents and readily silylates alcohols, acids, amines, thiols, phenols, hydroxamic acids, amides, thioamides, sulfonamides, phosphoric amides, phosphites, hydrazines, and enolizable ketones. It works best in the presence of a catalyst such as X-NH-Y, where at least one of the group X or Y is electron-withdrawing. ... 

Hexamethyidisilazane (HMDS) [999-97-3] M 161.4, b 125-125.6°/atm, 126°/760mm, d 0.7747, n 1.407. Possible impurity is Me3SiCl. Wash well with pet ether and fractionate through a vacuum jacketed column packed with Helipac using a reflux ratio of 10 1. [J Org Chem 23 50 1958.]... 

Phthalic anhydride, HMDS, rt, 1 h, then reflux with ZnBr21 h, 94% yield. ... 

Other PK variations include microwave conditions, solid-phase synthesis, and the fixation of atmospheric nitrogen as the nitrogen source (27—>28). Hexamethyldisilazane (HMDS) is also an excellent ammonia equivalent in the PK synthesis. For example, 2,5-hexanedione and HMDS on alumina gives 2,5-dimethylpyrrole in 81% yield at room temperature. Ammonium formate can be used as a nitrogen source in the PK synthesis of pyrroles from l,4-diaryl-2-butene-l,4-diones under Pd-catalyzed transfer hydrogenation conditions. 

Hexane-2,5-dione (342 mg, 3 mmol) was thoroughly mixed with alumina (1 g) before HMDS (1 mL, 4.8 mmol) was added, and the mixture was heated at 100-110 °C until the hexamethyldisiloxane formed was completely evaporated (about 20 min). Once the mixture cooled down to rt, the product was eluted with CH2CI2 and the oil obtained after evaporation of the solvent was purified by distillation yield 231 mg (81%), bp 68 °C/18 Torn... 

Procedure. Treat 10 mg of sucrose with 1 mL of anhydrous pyridine, 0.2 mL of HMDS, and 0.1 mL of TMCS in the plastic-stoppered vial (or similar container). Shake the mixture vigorously for about 30 seconds and allow it to stand for 10 min at room temperature if the carbohydrate appears to remain insoluble... 

Gas chromatographic analysis, using an HMDS-treated Chromo-sorb W column with 7% Craig polyester as the stationary phase, indicated the product to have a purity of 97%. The 3% impurity is most probably the isomeric 1-methylcyclohexene. 

The use of HMDS (ca. 1.5 mmol) and saccharin (0.01 mmol) per mmol of substrate in refluxing dichloromethane or chloroform has been recommended (5) for easy silylation of carboxylic acids, including azetidin-2-one-4-carboxyIic acids. Clear solutions result, i.e., no ammonium salts are present at completion of the reaction, and consequently the silyl esters can be obtained by direct distillation, or merely by evaporation of solvent. 

To a suspension of (45)-azetidin-2-one-4-carboxyIic acid (0.1 mol) and saccharin (1 g) in chloroform (200ml) was added HMDS (0.4mol), and the mixture was heated under reflux for 1.5 h. The excess HMDS was removed under reduced pressure, and the residue was distilled to afford the protected /1-lactam (0.089mol. 89%). b.p. 74-76 °C/0.08mmHg. 

To a mixture of the alcohol (0.2 mol) and HMDS (0.11 mol) was added two drops of TMSC1, and the solution was gradually heated to reflux over 1-2h. After an appropriate further time of reflux (ca. 4h for primary and 16 h for secondary), the reaction mixture was cooled and distilled. 

A solution of TMSC1 (0.07 mol) in hexane (10 ml) was added dropwise with stirring to a mixture of the alcohol (0.2mol) and HMDS (0.067mol). The resulting mixture was heated under reflux for 5h, cooled, filtered, and the precipitate was washed with pentane (2x50ml). The organic extracts were concentrated and the residue was distilled. 

Ammonolysis is the preferred route currently in use at the DuPont Company for the depolymerization of nylon-6,6 carpet waste. McKinney13 has described the reaction of nylon-6,6 and nylon-6 mixtures with ammonia at temperatures in the range of 300-350°C at a pressure of about 68 atm in the presence of an ammonium phosphate catalyst to form a mixture of nylon-6,6 and nylon-6 monomers (HMD A, A A, and s-caprolactam) and adiponitrile, 5-cyanovaleramide, 6-aminocapronitrile, and 6-aminocaproamide. 

Some advances have been made in the Paal-Knorr synthesis of pyrroles by the condensation of primary amines with 1,4-dicarbonyl species. For instance, a new synthetic route to monosubstituted succinaldehydes allows for the facile preparation of 3-substituted pyrroles <96TL4099>. Additionally, a general method for the synthesis of 1-aminopyiroles has been devised by the condensation of commercially available 2,2,2-trichloroethyl- or 2-(tri-methylsilyl)ethylhydrazine with 1,4-dicarbonyl compounds <96JOCl 180>. A related route to such compounds involves the reaction of a-halohydrazones with p-dicarbonyl compounds <96H(43)1447>. Finally, hexamethyldisilazane (HMDS) can be utilized as the amine component in the Paal-Knorr synthesis in the presence of alumina, and this modification has been employed in the synthesis of tm azaprostacyclin analog <96S1336>. 

The rates of radical-forming thermal decomposition of four families of free radical initiators can be predicted from a sum of transition state and reactant state effects. The four families of initiators are trarw-symmetric bisalkyl diazenes,trans-phenyl, alkyl diazenes, peresters and hydrocarbons (carbon-carbon bond homolysis). Transition state effects are calculated by the HMD pi- delocalization energies of the alkyl radicals formed in the reactions. Reactant state effects are estimated from standard steric parameters. For each family of initiators, linear energy relationships have been created for calculating the rates at which members of the family decompose at given temperatures. These numerical relationships should be useful for predicting rates of decomposition for potential new initiators for the free radical polymerization of vinyl monomers under extraordinary conditions. 

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