Toluene diisocyanate control

Yield for the process at low catalyst loading is 95%. AJ-Methyl-toluenediamiae, one of the reaction by-products, represents not only a reduction ia yield, but also a highly objectionable impurity ia the manufacture of toluene diisocyanate. Low concentrations of CO (0.3—6% volume) control this side reaction. 

Uses Preparation of 3,4-dichloroaniline solvent for a wide variety of organic compounds and for oxides of nonferrous metals solvent carrier in products of toluene diisocyanate intermediate for dyes fumigant insecticide for termites degreasing hides and wool metal polishes degreasing agent for metals, wood, and leather industrial air control disinfectant heat transfer medium. 

In the Montreal case-control study carried out by Siemiatycki (1991) (see monograph on dichloromethane in this volume), the investigators estimated the associations between 293 workplace substances and several types of cancer. Isocyanates were one of the substances, and it was stated that the most common form in this study was toluene diisocyanates. The main occupations to which isocyanate exposure was attributed in this study were motor vehicle refinishers, motor vehicle mechanics and foundry workers. Only 0.8% of the study subjects had ever been exposed to isocyanates. For most types of cancer examined (oesophagus, stomach, colon, rectum, pancreas, prostate, bladder, kidney, skin melanoma, lymphoma), there was no indication of an excess risk due to isocyanates. For lung cancer, in the population subgroup of French Canadians (the majority ethnic group in this region), based on 10 cases exposed at any level, the odds ratio was 2.2 (90% CI, 0.9-5.3). [The interpretation of the null results has to take into account the small numbers and presumably low exposure levels. Workers had multiple exposures.]... 

Ten days after a spill of 13 tons of toluene diisocyanate onto wet forest soil, the area was covered with sand. The soil concentration of toluene diisocyanate and toluenediamine declined from parts per thousand to parts per million from 10 days to 12 weeks after the spill. Six years later, only polyureas were found. Under controlled conditions, 5 kg of toluene diisocyanate was covered with 50 kg of sand and 5 kg of water and samples taken from the top and bottom of the sand. After 24 h, <6% toluene diisocyanate remained. Toluene diisocyanate is rapidly hydrolyzed... 

An example of a sequential-reaction extractive reaction is the manufacture of 2,4-dinitrotoluene, an important precursor to 2,4-diaminotoluene and toluene diisocyanate (TDl) polyurethanes. The reaction involves nitration of toluene by using concentrated nitric and sulfuric acids which form a separate phase. Toluene transfers into the acid phase where it reacts with nitronium ion, and the reaction product transfers back into the organic phase. Careful control of liquid-liquid contacting conditions is required to obtain high yield of the desired product and minimize formation of unwanted reaction products. A similar reaction involves nitration of benzene to mononitrobenzene, a precursor to aniline used in the manufacture of many products including methylenediphenylisocyanate (MDI) for polyurethanes [Quadros, Reis, and Baptista, Ind. Eng. Chem. Res., 44(26), pp. 9414-9421 (2005)]. 

Di-n-butyltin catalysts are being used in the preparation of polyurethane foams. Most polyurethane foams utilize aromatic isocyanates such as toluene diisocyanate (TDI) or diphenylmethane diisocyanate (MDI) as the isocyanate, and a polyester or polyether polyols as the coreactant. Tertiary amine catalysts are used to accelerate the reaction with water and formation of the carbon dioxide blowing agent. To achieve a controlled rate of reaction with the polyol, an organotin catalyst can be used. Polyurethane foams are not only applied in place, but are also cast in a factory as slabstocks. These foam slabs are then cut for use in car seats, mattresses, or home furnishings. DBTDL is an excellent catalyst in high resiliency slabstock foams. DBTDL shows an excellent reaction profile for this application replacement for DBTDL in such an end-use is difficult and requires a substantial reformulation of the foam. 

The modification of a filler surface with isocyanates is a simple process which involves the reaction of hydroxyl groups on the filler surface with monomeric isocyanate. 2,4-toluene diisocyanate or hexamethylene diisocyanate are commonly used. Since isocyanates are bifunctional they can be further reacted with polyols to form a coating on the surface or they can be used for the reinforcement of polyurethane. A strong covalent bonding can be verified by controlled extraction with the solvent. Bound material will not be removed from the fillefs surface. 

W. S. Toluene diisocyanate—engineering and medical control of exposures in polyurethane foam manufacturing. Am Ind Hyg Assoc g, 1957, 18, 331-34. 

Urethane-modified alkyds are similar to simple alkyds except that dibasic acid is replaced with a difunctional isocyanate such as toluene diisocyanate or hexamethylene diisocyanate. The process is also similar to simple alkyds. Coatings made with urethane-modified alkyds dry faster and harder than alkyds, yet retain flexibility. These systems have better water-, chemical- and abrasion-resistance than alkyd resins, and cost is also relatively low (Wicks et al., 1998). These are used in clear finishes for wood floors, cabinets, OEM, maintenance, and architectural coatings. The aliphatic-based systems are excellent for exterior use, or where UV exposure is possible, while aromatic-based systems usually have better abrasion-resistance. Chemo-enzymatic synthesis of urethane-based systems produces better control of stereochemistry and can impart unique properties (Athawale Bhabhe, 1998 Athawale Gaonkar, 1999 Athawale Joshi, 2000, 2004 Bhabhe Athawale, 1998). 

Figure 2.9 presents the results of a study of the surface tension of the POPT-based system. The polymerization level of the ohgomer was controlled by the amount of toluene diisocyanate (TDI) added to the system, the reaction of which with the polyester resulted in the formation of the polyurethane. Completion of the reaction and the system conversion level were monitored by IR spectroscopy using the change of the adsorption band in the region of 2280 cm that corresponds to isocyanate groups. The surface tension was measured at 90°C. 

The determination of residual monomer is frequently required in the quality control of polymers, and may easily be achieved by SEC. Toluene diisocyanate (TDI) in a polyurethane was determined by Spagnolo [43] by derivatization of the sample with ethanol, followed by SEC. 

DIAMINE CHAIN-EXTENDER CONTROL OF THE PHYSICAL PROPERTIES OF TOLUENE DIISOCYANATE-BASED ELASTOMERS... 

Flexible Polyurethane. These foams are produced from long-chain, lightly branched polyols reacting with a diisocyanate, nsnally toluene diisocyanate [1321-38-] (TDI), to form an open-celled structure with free airflow during flexure. During manufacture these foams are closely controlled for proper density, ranging from 13 to 80 kg/m (0.8-5 Ib/ft ), to achieve the desired physical properties and cost. 

PUs are synthesized by the reaction between isocyanates (conunonly DIs) and diols (or polyols), which results in the formation of carbamates. Depending on the diols or isocyanates used the mechanical/physical properties of the resulting polymers can be controlled. The most commonly used isocyanates are the aromatic DIs, toluene diisocyanate (TDl) and 4,4 -diphenytmethane diisocyanate (MDI). 

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