Catalysis in competing isocyanate reactions. I. Effect of organotin–tertiary amine catalysts on phenyl isocyanate and N-butanol reaction

An analytical method based on high performance liquid chromatography (HPLC) has been developed to investigate the competing isocyanate reactions under the influence of various catalysts. The kinetics of the model reaction between phenyl isocyanate and n-butanol was studied in acetonitrile at 50°C. Effects of various catalysts such as an organotin compound, dibutyltin dilaurate, and tertiary amines, 1,4-diazabicyclo-(2,2,2)octane,N,N′,N″-pentamethyldiprophylene triamine,N,N′N″-tris(3-dimethyl-aminopropyl)-3-hexahydrotriazine, and N,N,N′-trimethylaminoethyl-ethanolamine on the reaction rate and the formation of reaction products were investigated. The reactions were followed by determining the NCO disappearance using the standard di-n-butylamine back-titration method as well as measuring the formation of various reaction products using the HPLC method. The relative specificity of a catalyst in isocyanate reactions can thus be determined from the profile of the model reaction which depends upon the structure of the catalyst employed.     

Side Reactions in the Formation of Polyurethanes: Model Reactions Between Phenylisocyanate and 1-Butanol

The following side reactions occurring in the formation of polyurethanes were modeled: a reaction of excess phenyl isocyanate either with 1-butanol in 1, 4-dioxane and in bulk, or with n-butylphenyl urethane or water in dioxane catalyzed with dibutyltin dilaurate that leads to the formation of n-butyl-α, γ-diphenyl allophanate N, N-diphenylurea, and 1, 3, 5-triphenylbiuret. The reaction products were determined quantitatively by means of liquid chromatography. The rate and equilibrium constants were calculated at various temperatures and various initial ratios of functional groups. Biuret is formed from N, N'-diphenylurea much more quickly than allophanate from urethane, and the equilibrium constant of its formation is also higher.     

Solvent-assisted alcohol-isocyanate kinetics

The dependence of the reaction rate of cyclopentanol with phenyl isocyanate on the concentration of monomeric alcohol [1] in toluene, di-n-butyl ether and acetonitrile suggests a reaction scheme involving various complexes.     

Preparation and reactions of hydrophilic isocyanate micelles dispersed in water

We investigated the abnormal reaction behavior of NCO units in micellar hydrophilic isocyanate in water through titration, particle size, FT-IR spectroscopy and GPC and mechanical properties. Hexamethylene diisocyanate (HDI) allophanate was modified with methoxy polyethyleneglycol (MPEG), yielding novel hydrophilic isocyanate, which formed stable and homogeneous micelles in water. The results we obtained showed that the rapid reduction of the NCO group took place at a specific time (with an induction period) after dispersing hydrophilic isocyanate into water. The induction period, which is equal to the lifetime of the NCO group, was largely dependent on the diameter of micelles determined by the content of MPEG introduced. The result of GPC measurement indicated that there are three types of reactions between NCO groups and water. The rapid reduction of NCO in water was explained by the stepwise progress of the reactions, according to the location of NCO units in the core-shell structure of hydrophilic isocyanate micelles.     

Quantum-chemical study on reactions of isocyanates with methanol associates: VI. Quantum-chemical characterization of the relative reactivity of linear and cyclic methanol trimers in the addition to methyl isocyanate

Quantum-chemical study on the reaction of methyl isocyanate with cyclic methanol trimer at the B3LYP/6-311++G(df,p) level of theory showed that the process involves concerted asymmetric transition state in which the formation of new N-H bond outstrips the formation of new C-O bond. The reaction of methyl isocyanate with linear methanol trimer was found to be both kinetically and thermodynamically more favorable than with cyclic trimer.     

N-p-toluenesulfonyl-2-oxazolidones Via the cycloaddition reaction of p-tolucnesulfonyl isocyanate and epoxides

The reaction of styrene oxide and phenyl glycidyl ether with p-toluenesulfonyl isocyanate, employing a hydrocarbon-soluble adduct of tributylphosphine oxide and lithium bromide as catalyst, results in excellent yields of the N-p-toluenesulfonyl-2-oxazoIidones. The 5-isomeric-2-oxazolidone is obtained from phenyl glycidyl ether, but in contrast to conventional isocyanates, the p-toluenesulfonyl isocyanate, upon reaction with styrene oxide, produces the 4-isomeric 2-oxazolidone as the major product. The effect of the N-sulfonyl group on the nmr spectra of 2-oxazolidones is discussed.     

Quantum-chemical study on the reaction of phenyl isocyanate with linear methanol associates: II. Addition at the C=O bond

Addition of linear methanol associates at the C=O group of phenyl isocyanate involves a concerted cyclic asymmetric late transition state. The reaction is accompanied by formation of pre- and post-reaction complexes. Isomerization of intermediate methyl hydrogen phenylimidocarbonate into methyl phenylcarbamate is characterized by a considerable energy barrier. The reactivity of methanol molecules increases in parallel with the degree of their association, which is related to increase in their electron-donor power. Comparison of the calculated parameters for the addition of methanol associates at the C=N and C=O bonds of phenyl isocyanate clearly indicates that the first path is preferred.     

AC electrical conductivity measurements during H2-TPD experiments on a Pt/Al2O3 catalyst

The kinetics of the reaction of cyclopentanol with PhNCO or OCN(C₆H₁₂)NCO was studied in toluene, di-n-butyl ether and acetonitrile. The results suggest a predominant influence of the aggregation state of alcohol.     

Novel C-phosphorylated heterodienes based on pentachloroethyl isocyanate

A preparative method for the synthesis of novel N-phosphorylcarbonyl-and N-alkoxycarbonyltrichloroacetimidoylphosphonates from accessible pentachloroethyl isocyanate was developed. Factors that determine the C/N-selectivity of the phosphorylation of trichloroacetimidoyl chlorides were revealed: phenyl substituents at the P atom and an electron-withdrawing N-alkoxycarbonyl group in imidoyl chloride favored N-phosphorylation, while reactions with silyl phosphite gave exclusively C-phosphorylation products. Dedicated to the Corresponding Member of the Russian Academy of Sciences T. A. Mastryukova. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2563–2566, November, 2005.     

Studies in the formation of poly(oxazolidones) I. Kinetics and mechanism of the model oxazolidone formation from phenyl isocyanate and phenylglycidyl ether. Selectivity of catalysts

The reaction of phenyl isocyanate with phenylglycidyl ether in the presence of various catalysts served as a model reaction for the preparation of poly(oxazolidones). The type of catalyst used determines the mechanism of the oxazolidone synthesis. In addition to the basic product, oxazolidone, side products may be formed, the most frequent of which is the formation of isocyanurates, which depends upon the temperature and the type of catalyst. The most effective epoxide-soluble catalysts evaluated so far in the preparation of oxazolidones were the complex catalyst AlCl₃-triphenylphosphine oxide and AlCl₃-hexamethylphosphoric triamide. The kinetic study of the oxazolidone formation was carried out by means of HPLC, and the isocyanate and epoxide were separately determined by means of the di-n-butylamine and the perchloric acid methods, respectively. The HPLC method also clearly demonstrated the presence of two isomers, 3-phenyl-5-phenoxymethyloxazolidone-2 and 3-phenyl-4-phenoxymethyloxazolidone-2. The distribution of these isomers, previously reported in the literature, was found to depend upon the temperature and the type of catalyst used.     

Synthese und Kristallstruktur des trimeren [(Me3Si)2CH]2Al?CN

Synthesis and Crystal Structure of the Trimeric [(Me₃Si)₂CH]₂Al? CN Tetrakis[bis(trimethylsilyl)methyl]dialane(4) 1 with an Al? Al bond reacts with tert-butyl isocyanide in the molar ratio of 1:2 within three days to give a mixture of several unknown products, from which the title compound 4 is isolated in a 26% yield by recrystallization from n-pentane. 4 is a trimer in the solid state via Al? C?N? Al bridges showing a nine-membered Al₃C₃N₃ heterocycle in a boat conformation. In contrary to the reaction with phenyl isocyanide the expected dark red product of the twofold insertion into the Al? Al bond under formation of a carbon-carbon single bond is detected only spectroscopically as a minor by-product.     

One‐pot synthesis of isocyanate and methacrylate multifunctionalized polyisobutylene and polyisobutylene‐based amphiphilic networks

Amphiphilic polymer networks consisting of hydrophilic poly(2‐hydroxyethyl methacrylate) (PHEMA) and hydrophobic polyisobutylene (PIB) chains were synthesized from a cationic copolymer of isobutylene (IB) and 3‐isopropenyl‐α,α‐dimethylbenzyl isocyanate (IDI) prepared at ?50 °C in dichloromethane in conjunction with SnCl₄. The isocyanate groups of this random copolymer, PIB(NCO)_n, were subsequently transformed in situ to methacrylate (MA) groups in the dibutyltin dilaurate‐catalyzed reaction with 2‐hydroxyethyl methacrylate (HEMA) at 30 °C. The resulting PIB(MA)_n with number–average molecular weight 8200 and average functionality F_n ～ 4 per chain was in situ copolymerized radically with HEMA at 70 °C, giving rise to the amphiphilic networks containing 41 and 67 mol % HEMA. PHEMA–PIB network containing 43 mol % HEMA was also prepared by radical copolymerization of PIB(MA)_n precursor with HEMA using sequential synthesis. An amphiphilic nature of the resulting networks was proved by swelling in both water and n‐heptane. PIB(NCO)_n and PIB(MA)_n were characterized by FTIR spectroscopy, SEC and the latter also by ¹H NMR spectroscopy. Solid state ¹³C NMR spectroscopy was used for characterization of the resulting PHEMA–PIB networks. Whereas single glass‐transition temperature, T_g = ?67.4 °C, was observed for the rubbery crosslinked PIB prepared by reaction of PIB(NCO)_n with water, the PHEMA–PIB networks containing 67 and 41 mol % HEMA showed two T_g's: ?70.4 and 102.7 °C, and ?63 and 107.2 °C, respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2891–2900, 2006     

Nitrogen–Carbon Bond Formation by Reactions of a Titanium–Potassium Dinitrogen Complex with Carbon Dioxide,tert-Butyl Isocyanate,and Phenylallene

Nitrogen–carbon bond-forming reactions at coordinated dinitrogen in a bifunctional titanium–potassium system are reported. A titanium atrane complex with a tris(aryloxide)methyl ligand ( 1 ) was treated with two equivalents of potassium naphthalenide under N₂ atmosphere to generate a bifunctional complex ( 2 ) in which N₂ binds end-on to two titanium centers and side-on to three potassium cations. Dinitrogen complex 2 reacted with carbon dioxide, tert-butyl isocyanate, and phenylallene, forming nitrogen–carbon bonds and affording diverse N-functionalized products. The reaction of 2 with CO₂ followed by addition of Me₃SiCl resulted in the formation of the starting complex 1 with concomitant release of silylated carboxyl hydrazines while the reaction with two equivalents of tert-butyl isocyanate proceeded by insertion into the Ti−N bonds. Treatment of 2 with phenylallene afforded vinyl-substituted hydrazido complexes.     

Grafting onto carbon black by the reaction of reactive carbon black having masked isocyanate or acyl azide group with functional polymers

Although isocyanate group (NCO) introduced onto carbon black surface was inactivated rapidly upon storage, it could be stabilized by masking the NCO group with active hydrogen compounds such as acetylacetone, diethyl malonate, and sodium hydrogensulfite. Upon heating these carbon blacks having masked NCO group at 150°C, the NCO group was regenerated on carbon black by the decomposition of the masked NCO group. On the other hand, acyl azide (CON₃) group introduced onto carbon black was stable at below 20°C, but readily decomposed to NCO group by heating. By means of the reaction of NCO group on carbon black with functional polymers having hydroxyl, amino, and carboxyl group, these polymers were effectively grafted onto carbon black surface. When carbon black having CON₃ group was used as reactive carbon black, the grafting ratio of diol-type polyethylene glycol (M_n = 8.2 × 10³), polyethyleneimine (M_n = 2.0 × 10⁴), polyvinyl alcohol (M_n = 2.2 × 10⁴), and bifunctional carboxyl-terminated polystyrene (M_n = 1.1 × 10⁵) was determined to be 29.7, 81.7, 32.2, and 50.4%, respectively. The number of grafted polymer chain decreases with an increase in molecular weight of the polymers, because the shielding effect of NCO group by grafted polymer chain is enhanced with an increase in molecular weight of the polymer.     

Crosslinking polymerization leading to interpenetrating polymer network formation. I. Polyaddition crosslinking reactions of poly(methyl methacrylate‐co‐2‐methacryloyloxyethyl isocyanate)s with ethylene glycol resulting in polyurethane networks

At the start of our research program concerned with the elucidation of the crosslinking polymerization mechanism leading to interpenetrating polymer network (IPN) formation, in which IPNs consist of both polymethacrylates and polyurethane (PU) networks, this article deals with the polyaddition crosslinking reaction leading to PU network formation. Therefore, 2‐methacryloyloxyethyl isocyanate (MOI) was radically copolymerized with methyl methacrylate (MMA) in the presence of CBr₄ as a chain‐transfer agent. The resulting poly(MMA‐co‐MOI)s, having pendant isocyanate (NCO) groups as novel multifunctional polyisocyanates, were used for polyaddition crosslinking reactions with ethylene glycol as a typical diol. The second‐order rate constants depended on both the functionality of poly(MMA‐co‐MOI) and the NCO group concentration. The actual gel points were compared with the theoretical ones calculated according to Macosko's equation; the deviation of the actual gel point from the theoretical value became more remarkable for a greater functionality of poly(MMA‐co‐MOI) and at a lower NCO group concentration or at a lower poly(MMA‐co‐MOI) concentration. These are discussed mechanistically, with consideration given to the significance of intramolecular cyclization and intramolecular crosslinking reactions leading to the shrinkage of the molecular size of the prepolymer, along with the data of the intrinsic viscosities of resulting prepolymers and the swelling ratios of resulting gels. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 606–615, 2003     

Investigation of the competitive rate of derivatization of several secondary amines with phenylisocyanate (PHI), hexamethylene-1,6-diisocyanate (HDI), 4,4'-methylenebis(phenyl isocyanate) (MDI) and toluene diisocyanate (TDI) in liquid medium

The stabilization of the isocyanate (NCO) groups during workplace sampling is necessary for their subsequent laboratory analysis. Most derivatization reagents are secondary amines. By carrying out a test in which two secondary amines are added to an isocyanate, the relative rates of these reactions can be evaluated. This evaluation is known for a monoisocyanate, phenylisocyanate (PHI), but is being developed for diisocyanates. This study deals with the relative reactivity (RR) of four diisocyanates: hexamethylene 1,6-diisocyanate (HDI), 4,4'-methylenebis(phenyl isocyanate) (MDI), and the ortho and para isomers of toluene diisocyanate (TDI) in addition to PHI, with four secondary amines: 1-(2-methoxyphenyl)piperazine (MOPIP), 9-(N-methylaminomethyl)anthracene (MAMA), 1-(9-anthracenylmethyl)piperazine (MAP), and dibutylamine (DBA). These competitive derivatization reactions are studied in three reaction solvents, namely acetonitrile, toluene, and acetonitrile doped with water (1% v/v). The results show that the order of reactivity, which doesn't change with the isocyanate as well as with the solvent used, is the following: DBA > MAP > MOPIP > MAMA. The relative difference in reactivity is a function of both the isocyanate and the solvent used. Hindered aromatic diisocyanates (TDI and MDI) show a greater difference in reactivity with the derivatization agents. These differences in reactivity are also modified by the solvent used. For example, larger differences are observed in acetonitrile than in toluene, but the introduction of water to acetonitrile, which does not affect the reaction yield, makes these differences smaller.     

Studies in tertiary amine oxides. III—carbon-13 NMR assignment of N-alkynyl cyclic amines

Carbon-13 NMR spectra of 24 N-alkynyl cyclic amines were analysed. The effect of substituting the acetylenic proton by n-butyl, tert-butyl and phenyl groups was determined.     

Synthesis of 3-alkoxycarbonylaminomethylcarbonylamino-4-benzoyl-1,2-dihydropyridines and their cyclization to 5-phenyl-1,3,8,9-tetrahydro-2H-pyrido[3,4-e]-1,4-diazepin-2-ones

The regiospecific reaction of 3-benzyloxycarbonylaminomethylcarbonylamino-4-benzoylpyridine (6a) , or 3-t-butoxycarbonylaminomethylcarbonylamino-4-benzoylpyridine (6b) , with either acetyl chloride or ethyl chloroformate, and either n-butylmagnesium chloride or phenylmagnesium bromide afforded the respective 1-acetyl (or ethoxycarbonyl)-2-n-butyl (or phenyl)-3-benzyloxy (or t-butoxy) carbonylaminomethylcarbonylami-no-4-benzoyl-1,2-dihydropyridines 7 in 60-75% yield. Reaction of 1-acetyl (or ethoxycarbonyl)-2-n-butyl (or phenyl)-3-t-butoxycarbonylaminomethylcarbonyl-4-benzoyl-1,2-dihydropyridines 7b, 7f, 7d, 7h with trifluoroacetic acid gave the corresponding 5-phenyl-8-acetyl (or ethoxycarbonyl)-9-n-butyl (or phenyl)-1,3,8,9-tetrahydro-2H-pyrido[3,4-e]-1,4-diazepin-2-ones 8a, 8b, 8c, 8d respectively in 45–63% yield. N¹-Methylation of 5-phenyl-8-acetyl-9-n-butyl (or phenyl)-1,3,8,9-tetrahydro-2H-pyrido[3,4-e]-1,4-diazepin-2-ones 8a, 8b using sodium hydride and iodomethane yielded the corresponding N¹-methyl derivatives 9a (48%) and 9b (54%). Oxidation of 5,9-diphenyl-8-ethoxycarbonyl-1,3,8,9-tetrahydro-2H-pyrido[3,4-e]-1,4-diazepin-2-one (8d) using p-chloranil afforded 1,3-dihydro-5,9-diphenyl-2H-pyrido[3,4-e]-1,4-diazepin-2-one (10) . 5-Phenyl-8-acetyl-9-n-butyl-1,3,8,9-tetrahydro-2H-pyrido[3,4-e]-1,4-diazepin-2-one (8a) and the corresponding 8-ethoxycarbonyl analog 8c exhibited weak anticonvulsant activity indicating that 8a and 8c may be acting at the same site as the 7-halo-1,4-benzodiazepin-2-one class of compounds.     

Exchange reactions of urethanes with proton-donating compounds: Kinetics of the reactions of phenyl-<Emphasis Type="Italic">N</Emphasis>-phenylurethane with butyl alcohols

The exchange reactions of phenyl-N-phenylurethane with aliphatic alcohols, namely, n-butyl, sec-butyl, and tert-butyl alcohols, in ortho-dichlorobenzene and in the media of the corresponding alcohols were studied. In the absence of a catalyst and proton-donating compounds, the monomolecular cleavage of phenyl-N-phenylurethane to isocyanate and alcohol proceeds at a noticeable rate starting only at 250°C. Between 40 and 80°C, the exchange reactions take place via direct exchange between urethane and the photon-donating compound and are second-order up to high conversions (until the almost complete disappearance of the initial urethane). Activation energies and apparent rate constants have been determined for the exchange reactions of phenyl-N-phenylurethane with butyl alcohols. The rates of the exchange reactions in the alcohol medium are compared with those in ortho-dichlorobenzene.     

Gas-phase thermolysis of sulfur compounds. Part III: n-butyl 2-propenyl sulfide

The pyrolysis of n-butyl 2-propenyl sulfide has been investigated in a static system in the initial pressure range of 50–350 torr. The reaction was found to be homogeneous and first order. The rate coefficients are given by the Arrhenius equation between 262 and 293°C. The rate of the reaction remains unchanged in the presence of cyclohexene as radical inhibitor. The main reaction products were propene and a trimer of n-butyl thioaldehyde. The results are interpreted in terms of a molecular mechanism involving a cyclic six-centered transition state. This mechanism is supported by the pyrolysis of 1,1-dideutero-n-butyl 2-propenyl sulfide at 281°C. The kinetic deuterium isotope effect had a value of 2.7 ± 0.2. Nuclear magnetic resonance and mass spectroscopic analysis of the reaction products showed the deuterium to be distributed as expected from the proposed reaction mechanism.