Carbonyl diisocyanate

Pyrolysis approaches can also be used to prepare substituted isocyanates which caimot be prepared using other methods. For example, A[,A[(A[ -trichlorocyanuric acid [87-90-1] thermally dissociates to yield chloroisocyanate [13858-09-8] and carbonyl diisocyanate [6498-10-8]. The carbonyl isocyanate is unstable and polymerizes (8,94). Table 3 Hsts specialty isocyanates. 

Treatment of trichloroisocyanuric acid (or sodium dichloroisocyanurate) with phosgene at 150-250 "C in 1,3,5-trichlorobenzene or 1,2-dichlorobenzene affords carbonyl diisocyanate, CO(NCO)j, in almost quantitative yield [616] ... 

A mixture of phosgene and carbonyl diisocyanate will undergo a comproportionation reaction at 180 C, to give a 56% yield of the mixed product [1018] ... 

This seems a reasonable mechanism, as the reaction of MCgSiCNCS) with phosgene gives CO(NCS)j [45a] and the reaction of tributyltin(IV) isocyanate with phosgene has been utilized for the synthesis of carbonyl diisocyanate [22a] ... 

Carbonyl diisocyanate (119) adds to iV-substituted amides to yield the unstable but isolable 1,3,5-oxadiazine-2,4(3//)-diones (120). However, with primary amides the resulting 1,3,5-oxa-diazinediones (120 = H) undergo a Dimroth rearrangement to the isomeric l,3,5-triazine-2,4,6-... 

Treatment of carbonyl diisocyanate with A-substituted amides or with alkyl carboxylic acids produces l,3,5-oxadiazine-2,4-diones (see Section 6.18.10.1.1), which are also prepared by base-catalyzed cyclocondensation of aroyl isocyanates with aryl isocyanates (see Section 6.18.10.2.2.i). 

Carbonyl diisocyanate (234) has been prepared and chlorinated to give (235). Reaction of this product with amines gives... 

Carbonyl diisocyanate (46) was shown to undergo a Diels-Alder type of cycloaddition with azomethines to give 2,3,6,7-tetrahydro-4/7,8/7-[l,3,5]triazino[2,l-Z>][l,3,5]oxadiazin-4,8-diones (16) (Scheme 5). A large variety of the triazino[2,l-ft][l,3,5]oxadiazines were realized by the suitable selection of dienophiles. Thus, l,3,5-triazino[2,l-Z>][l,3,5]oxadiazines (17), (18 R = NMe), and (19) and were synthesized by the reaction of carbonyl diisocyanate with alkyl or aryl isocyanates, dimethyl cyanamide, or aliphatic carbodiimides, respectively <86CB1133>. Due to the high reactivity of the cumulated double bonds, carbonyl diisocyanate (46) was also found to undergo [4 + 2] cycloadditions with cyclohexanone to yield cyclohexan-l-spiro-9 -[l,3,5]-oxadiazino-[3,4-e][l,3,5j-dioxazin-5 -spiro-l"-cyclohexane-2, 7 -dione (47) (Scheme 6) <76LA1634>. 

The homopol5unerization of diisocyanates is only useful for specialty diisocyanates, such as aliphatic 1,2- or 1,3-diisocyanates (3) and aromatic o-diisocyanates (4), which polymerize via cycloaddition processes. Anionic homopolymerization of monoisocyanates takes place by addition across the 0=N bond to form nylon-1 polymers. Polyamides are also obtained fi"om diisocyanates and enamines or ketenaminals. This reaction proceeds by a [2 -i- 2] cycloaddition reaction with subsequent ring opening to form polyamides. [2 - - 4] cycloaddition polymerization to form heterocyclic polymers is observed with carbonyl diisocyanate (5). Ring-opening polymerization occurs in the reaction of bis-epoxides... 

The reaction of phenyl isocyanate with t-butyl-A-(2,6-dimethylphenyl)imidoyl isocyanate proceeds similarly. A double [4+2] cycloaddition occurs in the reaction of carbonyl diisocyanate with aliphatic isocyanates to give l,3,5-triazino[2,l-b]-l,3,5-oxadiazine tetrones 471. ... 

Similar cycloadducts are obtained from carbonyl diisocyanate and azomethines, isocyanates, carbodiimides and dimethylcyanamide. 

Reductive carbonylation of nitro compounds (in particular aromatic dinitro compounds) is an important target in industry for making diisocyanates, one of the starting materials for polycarbamates. At present diisocyanates are made from diamines and phosgene. Direct synthesis of isocyanates from nitro compounds would avoid the reduction of nitro compounds to anilines, the... 

Two final examples of the sensitivity and general applicability of the FTIR gas analysis technique are illustrated in Fig. 8. Trace (A) shows the spectrum obtained from an ultra-air filled 70 liter sampling bag into which had been injected, 18 hours previously, 4.8 microliters of TDI, toluene diisocyanate. On the basis of the single feature at 2273 cm l, it is estimated that 50 ppb TDI could be detected. The lower Trace (B), shows the spectrum of nickel carbonyl. This highly toxic but unstable gas was found to decay rapidly at ppm concentrations in ultra air (50% lifetime 15 minutes). Calibration of its spectrum was established by recording successive spectra at ten minute intervals and by attributing the increase in carbon monoxide concentration (calibration known) to an equivalent but four times slower decrease in nickel carbonyl concentration. The spectrum shown represents 0.6 ppm of the material. Note the extraordinary absorption strength. The detection limit is thus less than 10 ppb. 

Specialty Isocyanates. Specialty isocyanates are organic isocyanates having the isocyanate function attached to a carbonyl group or to elements other than carbon. /t-Toluenesulfonyl isocyanate is used as a drying agent for organic solvents. Arenesulfonyl diisocyanates, such as m-phenylenedisulfonyl diisocyanate, are used as monomers for base-soluble polymers. Arenesulfonyl monoisocyanates are used as intermediates for pharmaceuticals and herbicides. 

The above processes are only selected examples of a vast number of process options. In the case of carbonylation, the formation of by-products, primarily isocyanate oligomers, allophanates, and carbodiimides, is difficult to control and is found to greatly reduce the yield of the desired isocyanate. Thus a number of nonphosgene processes have been extensively evaluated in pilot-plant operations, but none have been scaled up to commercial production of diisocyanates primarily due to process economics with respect to the existing amine—phosgene route. Key factors preventing large-scale commercialization include the overall reaction rates and the problems associated with catalyst recovery and recycle. 

Succinimides and maleimides are accessible via processes analogous to those described for the corresponding anhydrides (see Section 9.4.3.3). Reactions of (COD)2Ni° with either alkenes or alkynes and isocyanates (i.e. heterocumulene analogs of CO2) give azametallacycles that upon carbonylation yield cyclic imides. With alkenes high yields of metallacycles are formed m both simple isocyanates as well as a,(o-diisocyanates. Carbonylation yields are variable, however (Scheme 18). Alkynes give lower metallacycle yields but high yields of die final imide (Scheme 19). ... 

This process was elaborated as a heterogeneously catalyzed variation by Asahi Chemicals (Japan) in order to open a new route to diisocyanates, not depending on the use of phosgene [120, 134]. Ethyl phenylcarbamate, which in a first step is obtained by catalytic oxidative carbonylation of aniline, CO, oxygen, and ethanol (eq. (17)), is condensed with aqueous formaldehyde to yield methylene diphenyl diurethane. Thermal decomposition leads to methylene diphenyl diisocyanate (MDI), which is one of the most important intermediates for the industrial manufacture of polyurethanes (eq. (18)). The yields and selectivities of the last reaction step seem to be the main reasons why this process is still inferior to the existing ones. 

The primary product is aniline (eq. (8)), which then undergoes addition of carbonyl selenide, Se=C=0, in the presence of a strong base [17]. The resulting urethane can further be converted into the methylene diurethane, which is then cracked to the diisocyanate MDI 2, a key industrial intermediate for the production of polyurethane foams and elastomers (cf. Section 3.3.5). It was probably for toxicity reasons that completion of a technical plant at one of the Arco sites [18] was hampered. 

Plastics with a carbonyl group can be converted to monomers by hydrolysis or glycolysis. Condensation polymers such as polyesters and nylons can be depolymerized to form monomers. For Polyurethanes (PURs), what is obtained is not the initial monomer, but a reaction product of the monomer diamine, which can be converted to diisocyanate. For PURs. hydrolysis is attractive as they can be easily broken down to polyols and diamines. The only issue is to separate them later. Steam-assisted hydrolysis has been shown to yield 60 to 80 percent recovery of polyols from PUR foam products. A twin screw extruder can be used as a reactor for hydrolysis. Glycolysis of PURS, yields mixture of polyols that can be reused directly. 

Because of the increased commercial interest in diisocyanates [85,91], new manufacturing routes without the costly phosgenation step (i.e, without total loss of chlorine as HC1) have been developed. Processes for the catalytic carbonylation of aromatic nitro-compounds or amines are the most likely to become commercially important. 

Another manufacturing process [9l] for 4,4 -diphenylmethyl diisocyanate (MDI) was introduced by Asahi Chemical. In contrast to the ARCO route, aniline is used for the carbonylation to N-phenylethyl urethane otherwise, the same steps are followed. The oxidative carbonylation of aniline is done in the presence of metallic palladium and an alkali iodide promoter at 150-180°C and 50-80 bar. The selectivity is more than 95% with a 95% aniline conversion ... 

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