Isocyanate catalyst reactions with

Reactions with Isocyanates, TYZOR TPT catalyzes the trimerization of isocyanates and polyisocyanates to isocyanurates and polyisocyanurates (38). Titanium alkoxides of the type Cl3TiOR initiate the living polymerization of isocyanates. Polyisocyanates possessing controlled molecular weights and narrow polydispersities can be synthesized using these catalysts (39) ... 

If the reaction NO + CO is carried out at 200 to 400°C with Pt/Si02 catalyst separated by 8 to 10 mm from a wafer of pure Si02, the band at 2310 cm-1 which is characteristic of Si NCO is not detected on the silica wafer. The spillover of -NCO from Pt to Si02 therefore cannot proceed through the gas phase (158). But isocyanate on pure silica may also be formed by the reaction with isocyanic acid (HNCO) between 100 and 400°C. Now on Pt/Si02, -NCO is formed on Pt even at — 83°C (band at 2180 cm- J), which shows a dissociative adsorption of isocyanic acid on Pt ... 

It appears that the nucleophilic character of the active hydrogen compounds enables them to act also as their own catalysts in their reaction with isocyanates. On the whole their catalytic activity increases with the availability of the free electron pair. 

Wicks has reviewed the various reaction mechanisms with blocked isocyanates. There are two general mechanisms (addition-elimination and elimination-addition) by which the blocked isocyanate reacts with a hydroxyl compound (Figure 6.2.11, A and B). It is possible that a particular type of blocked isocyanate can function by either mechanism, depending on such factors as the type of blocking group, type of hydroxyl compound, temperature, and the polarity of the solvent. Tin catalysts such as DBTDL are often included in such formulations, but higher concentrations are required than in reactions with isocyanates and the role of the catalyst is not always well defined. 

The presence of the electron donor (-0-) in the vicinity of the phenolic hydroxyl activated the -OH group through induced polarization due to hydrogen bonding and therefore, increased reactivity was observed. Similarly, the polarizability of the phenolic hydroxyl groups by the tertiary amine catalyst is responsible for the multi order (1200 x) increase in the reactivity compared to the non-catalyzed reaction with isocyanate (see Table IV)... 

Kuninobu has found that benzaldimines undergo C-H activation and acetylene insertion to give indenes using a rhenium catalyst (Equation (43)). A similar reaction with isocyanates gives rise to phthalimidine derivatives (Equation (44)). " This catalyst also efficiently permits insertion of terminal alkynes into the acidic C-H bond of 1,3-diketones to give branched vinyl products. 

The properties of polyurethanes derived from the hydroformylation of fatty acid derivatives, subsequent hydrogenation, and reaction with isocyanates such as toluene diisocyanate (TDl), methylene diphenyl-4,4-diisocyanate (MDI), and 1,6-hexamethylenediisocyanate (HDI) may be strongly dependent on the metal used for the hydroformylation [12a, 62]. At high conversion rates with a rhodium catalyst, a rigid polyurethane A is formed, whereas under the conditions of cobalt catalysis and low conversion a hard rubber or rigid plastic (polyurethane B) with lower mechanical strength results (Scheme 6.100). 

Imines also undergo [2-I-2-I-2] cycloaddition reactions with isocyanates. Usually, one equivalent of the imine reacts with two equivalents of the isocyanate. For example, heating of an excess of azomethines or benzophenone anils with isocyanates affords six-membered ring [2+2- -2] cycloadducts (see Section 3.3.1.4). This reaction proceeds in a stepwise manner, as indicated by the formation of different cycloadducts when different isocyanates are used. Also, reaction of A-alkyl- and A-aryl formamidines with alkyl- or aryl isocyanates on heating or in the presence of zinc chloride as the catalyst gives 2 1 (iminedsocyanate) adducts. Some examples of these reactions are listed in Table 3.10. 

Similarly, thioalcohols and thiophenols react with isocyanates to form thiocarbamates. Although these reactions are generally found to be much slower than that of the corresponding alcohol, alkoxide catalysts have successfully been used to provide moderate levels of rate enhancement (68). 

Organic Derivatives. Although numerous mono-, di-, and trisubstituted organic derivatives of cyanuric and isocyanuric acids appear in the hterature, many are not accessible via cyanuric acid. Cyanuric chloride 2,4,6-trichloro-j -triazine [108-77-0], is generally employed as the intermediate to most cyanurates. Trisubstituted isocyanurates can also be produced by trimerization of either aUphatic or aromatic isocyanates with appropriate catalysts (46) (see Isocyanates, organic). Alkylation of CA generally produces trisubstituted isocyanurates even when a deUberate attempt is made to produce mono- or disubstituted derivatives. There are exceptions, as in the production of mono-2-aminoethyl isocyanurate [18503-66-7] in nearly quantitative yield by reaction of CA and azitidine in DMF (47). 

The allophanate linkage is formed by the reaction of urethane with isocyanate, as shown in the fourth item of Fig. 1 [7], Isocyanates can react with many active hydrogen compounds. The active hydrogen of the urethane linkage is not very reactive, but if reaction temperatures get high enough (usually in excess of 100°C), or in the presence of certain allophanate catalysts, this reaction can actually become favored over the urethane reaction (see pp. 180-188 in [6]). 

There are actually three reactions called by the name Schmidt reaction, involving the addition of hydrazoic acid to carboxylic acids, aldehydes and ketones, and alcohols and alkenes. The most common is the reaction with carboxylic acids, illustrated above.Sulfuric acid is the most common catalyst, but Lewis acids have also been used. Good results are obtained for aliphatic R, especially for long chains. When R is aryl, the yields are variable, being best for sterically hindered compounds like mesi-toic acid. This method has the advantage over 18-13 and 18-14 that it is just one laboratory step from the acid to the amine, but conditions are more drastic. Under the acid conditions employed, the isocyanate is virtually never isolated. 

Waste PETP was depolymerised by glycolysis to give hydroxyl-terminated oligomers(DPET), which were used in the synthesis of urethane oils. The effect of depolymerisation temps., the type of glycol and the amount of catalyst on the yield and composition of the depolymerisation products was studied. The physical properties of the urethane oils were compared with those of a commercially-available product. The reaction of DPET with isocyanates produced random linkage between different molecules with or without terephthaloyl groups. 15 refs. 

Other authors also determined by FTIR that organic nitrocompounds are formed as primary products of the NO CH4-SCR reaction on ZSM-5-based catalysts [121-124], They preadsorbed nitromethane on the sample placed in the IR cell and followed by IR its transformation into other intermediates under 02 and NO versus time at different temperatures. For Cu- and Co-ZSM-5, it was shown that around 300°C adsorbed nitromethane is easily converted into isocyanates and then melamine via polymerization of the former species. Both species easily interact with molecular oxygen, while no reaction with NO is observed and the reactivity depends on the temperature and the nature of the transition metal cation. 

Yen and Chu subsequently also disclosed a related Pictet-Spengler reaction involving tryptophan and ketones for the preparation of 1,1-disubstituted indole alkaloids [417]. In the approach shown in Scheme 6.234, tryptophan was reacted with numerous ketones (12 equivalents) in toluene in the presence of 10 mol% of trifluoroacetic acid catalyst. Using microwave irradiation at 60 °C under open-vessel conditions, the desired products were obtained in high yields. Compared to transformations carried out at room temperature, reaction times were typically reduced from days to minutes. Subsequent treatment with isocyanates or isothiocyanates led to tetrahydro-/8-carbolinehydantoins. 

Subsequent experiments on the same system aimed to determine the stability of the isocyanate species and to measure the reactivity of the Pd(lll) model catalyst for the CO + NO reaction.125 When exposing the sample to different CO/NO ratios (2 and 1.5) at room temperature, peaks were obtained which corresponded to threefold NO, atop NO, and threefold CO, with the higher CO/NO ratio leading to a greater amount of CO binding. When the samples were flashed to 650 K and cooled back to 300 K in the presence of the reaction mixtures, isocyanate was formed. However, as is apparent from Figure 10.25, an increase in the CO/NO ratio strongly favored isocyanate formation. 

Alkyl and glycosyl isocyanates and isothiocyanates are produced in good yield under phase-transfer catalytic conditions using either conventional soluble catalysts or polymer-supported catalysts [32, 33]. Acyl isothiocyanates are obtained under similar conditions [34]. A-Aryl phosphoramidates are converted via their reaction with carbon disulphide under basic conditions into the corresponding aryl isothiocyanates, when the reaction is catalysed by tetra-n-butylammonium bromide [35]. 

The next study of wood modification was that reported by Baird (1969), who performed vapour-phase reactions of spruce with ethyl, n-butyl, /-butyl, allyl and phenyl isocyanate (PhNCO). Unfortunately, DMF was used as a catalyst for the reactions, which resulted in polymerization of PhNCO in the cell wall of the wood, leading to unpredictable results. No evidence was presented in support of the contention that polymerization had occurred, and since this requires an anionic catalyst initiator, this is considered unlikely. However, the presence of side reactions when DMF is used in conjunction with isocyanates has already been mentioned. Greater success was reported when butyl isocyanate was reacted with wood (presumably a consequence of the lower reactivity of this isocyanate... 

A study of the reaction kinetics of the reaction of butyl isocyanate with wood has been performed (West and Banks, 1986 West and Banks, 1987). Reactions were performed without catalyst and using pyridine, triethylamine, 1,4-diazobicyclo [2,2,2-octane] or di-butyl-tin-diacetate as catalyst. The data showed that no catalyst was effective without the presence of a swelling solvent. Kinetic profiles were obtained, which were deconvo-luted to yield two component reaction curves. It was considered that these two curves represented reaction with lignin and the holocellulose component of the cell wall. 

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