Phosgene, catalytic synthesis

Phonon broadening, 34 247,253 Phosgene, catalytic synthesis, 28 270-273 Phosphanes aliphatic, 42 493 hydroxyalkyl-substituted, 42 482 quaternary ammonium, 42 492 sugar derivatives, 42 482-483 sulfonated, 42 476-478 Phosphanorbomadienes... 

Desorption of CO from the surface of such charcoal occurs only at temperatures much higher than those employed in phosgene catalytic synthesis therefore, stage 1 of scheme (371) is irreversible under the usual conditions of the reaction. Kinetic measurements show that the reaction is retarded... 

The major advantage of this one-step catalytic synthesis is that no phosgene derivative such as R jNCOCI is used, which is greener than the traditional stoichiometric processes. It also enables straightforward access to vinylcarbamates, which are useful monomers for functional polymer production. 

Dinitrogen is continuously introduced into the reactor to remove the CH3OH overhead. By this procedure recombination of the isocyanate and alcohol is minimized. The dinitrogen stream is then used to strip any TDI fromlhe final reactor bottoms. Cutting chlorine out of the reaction (phosgene is avoided) is considered to reduce the cost of about 25-30% [234. Many systems are now known to catalyze reaction (81) and similar reactions. The most significant examples are reported on table X. As for the catalytic synthesis of isocyanates (4.2.5.) palladium, and to a lesser extent rhodium, are the metals more employed. 

Catalysis. Catalytic properties of the activated carbon surface are useful in both inorganic and organic synthesis. For example, the fumigant sulfuryl fluoride is made by reaction of sulfur dioxide with hydrogen fluoride and fluorine over activated carbon (114). Activated carbon also catalyzes the addition of halogens across a carbon—carbon double bond in the production of a variety of organic haUdes (85) and is used in the production of phosgene... 

A recent patent application describes, in part, a multikilogram scale synthesis of quinapril (Jennings, 2004). The carboxyanhydride of 26 is prepared by treatment with phosgene (Scheme 10.8) (Youssefyeh et al., 1987). This is next coupled with tetrahydroisoquinoline subunit 27 in the presence of catalytic acid. Without isolation of the resultant quinapril t-butyl ester, the reaction solution is treated with acetic acid and anhydrous hydrogen chloride to deprotect the ester. Amorphous quinapril hydrochloride is obtained via treatment with acetonitrile. 

The synthesis of a triptan with a chiral side chain begins by reduction of the carboxylic acid in chiral 4-nitrophenylalanine (15-1). The two-step procedure involves conversion of the acid to its ester by the acid chloride by successive reaction with thionyl chloride and then methanol. Treatment of the ester with sodium borohy-dride then afford the alanilol (15-2). Reaction of this last intermediate with phosgene closes the ring to afford the oxazolidone (15-3) the nitro group is then reduced to the aniline (15-4). The newly obtained amine is then converted to the hydrazine (15-5). Reaction of this product with the acetal from 3-chloropropionaldehyde followed by treatment of the hydrazone with acid affords the indole (15-6). The terminal halogen on the side chain is then replaced by an amine by successive displacement by means of sodium azide followed by catalytic reduction of the azide. The newly formed amine is then methylated by reductive alkylation with formaldehyde in the presence of sodium cyanoborohydride to afford zolmitriptan (15-7) [15]. 

The operation of the catalytic reactor was demonstrated by the synthesis of phosgene starting from carbon monoxide and chlorine. The experimental set-up is shown in Figure 3.33. 

The thermal synthesis of phosgene involves the reaction of carbon monoxide with dichlorine Equation (5.1) induced by purely thermal, as opposed to catalytic (Section 5.1.3), means. 

The thermal dissociation of phosgene into carbon monoxide and elemental chlorine. Equation (8.2), is the reverse of the reaction used widely, either thermally, catalytically or photochemlcally promoted, for the synthesis of phosgene (see Section 5.1). Thus, much of the chemistry relevant to this Section has already been covered in Chapters 5 and 6. Much of the early work, both kinetic and thermodynamic, was marred by a lack of appreciation of the importance of high purity, and the fact that the system takes a very long time to come... 

Desulfurization of petroleum feedstock (FBR), catalytic cracking (MBR or FI BR), hydrodewaxing (FBR), steam reforming of methane or naphtha (FBR), water-gas shift (CO conversion) reaction (FBR-A), ammonia synthesis (FBR-A), methanol from synthesis gas (FBR), oxidation of sulfur dioxide (FBR-A), isomerization of xylenes (FBR-A), catalytic reforming of naphtha (FBR-A), reduction of nitrobenzene to aniline (FBR), butadiene from n-butanes (FBR-A), ethylbenzene by alkylation of benzene (FBR), dehydrogenation of ethylbenzene to styrene (FBR), methyl ethyl ketone from sec-butyl alcohol (by dehydrogenation) (FBR), formaldehyde from methanol (FBR), disproportionation of toluene (FBR-A), dehydration of ethanol (FBR-A), dimethylaniline from aniline and methanol (FBR), vinyl chloride from acetone (FBR), vinyl acetate from acetylene and acetic acid (FBR), phosgene from carbon monoxide (FBR), dichloroethane by oxichlorination of ethylene (FBR), oxidation of ethylene to ethylene oxide (FBR), oxidation of benzene to maleic anhydride (FBR), oxidation of toluene to benzaldehyde (FBR), phthalic anhydride from o-xylene (FBR), furane from butadiene (FBR), acrylonitrile by ammoxidation of propylene (FI BR)... 

Another elimination reaction sequence, utilizing chlorodimethyl-formiminium chloride as catalyst, involves the synthesis of isocyanates by phosgenating carbamates XVI ( ). Thus, phosgene is used to generate the iminium chloride XVII, which reacts with XVI to form the chloro-imidate XVIII. The isolated isocyanate is formed by thermolysis of XVIII. Since N,N-dimethylformamide is regenerated, only a catalytic amount is necessary. 

By analogy with the general synthesis of imidoyl chlorides it can be expected that carbamates and thiocarbamates undergo reaction with a variety of acid halides to afford 1-haloformimidates and 1-halothio-formimidates, respectively. For example, carbamates have been reacted with carbonyl chloride ( ), pyrocatecholphosphorus trichloride ( ), and phosphorus pentachloride ( ), and isocyanates were obtained. In view of the catalytic effect of N,N-dimethylformamide in the phosgenation of carbamates to isocyanates, the intermediacy of 1-chloroformimidates X is anticipated ( ). 

The classical method -for carryng out the synthesis o-f isocyanates is V i a catalytic hydrogenation o-f nitro compounds and subsequent reaction with phosgene T4J ... 

The synthesis o-f MDI (methyl ened I phenyl di i socyanate, one o-f the most important monomer -for the production o-f pol yurethanes together with TDI, 2,4-toluenediisocyanate) without phosgene, has been carried out v i a the catalytic oxidative carbonyl at i on o-f aniline 73 ... 

The catalytic carbonylation of nitro compounds is a field of great interest, as a number of important industrial products can be produced (Scheme 9.1), [1-4] such as the synthesis of isocyanates, carbamates, ureas, etc., which normally needed toxic phosgene as the reaction reagent and can be replaced by cheap CO in the case of carbonylation of nitro compounds. After decades developments, several transition metals are known to be active for this transformation—for example, palladium, rhodium, ruthenium, and even iron, cobalt and selenium—all of which will be discussed in this chapter. 

The DuPont process not only eliminates the use of phosgene as a starting material, but also avoids the production of large amounts of hydrochloric acid as an unwanted by-product. In this method, methyl-amine reacts with carbon monoxide to yield the corresponding aldehyde, which is then catalytically converted to isocyanate. This phosgene-free replacement synthesis also supports the trend in the chemical process industry to seek to reduce inventories on plant sites of hazardous synthetic reagents. Methyl isocyanate produced from this process is converted in situ to an agrochemical product. 

The classical method for carrying out the synthesis of isocyanates includes the intermediate catalytic hydrogenation of the nitro compounds, and subsequent reaction of the product aniline with phosgene (eqs. 1 and 2) [9] ... 

The synthesis of MDI (methylenediphenyidiisocyanate, one of the most important monomers for the production of polyurethanes together with TDI, 2,4-toluendiisocyanate) without phosgene has been carried out via the catalytic oxidative carbonylation of aniline (Scheme 1) [11, 12] ... 

Sakakura et al. (150) have investigated the use of SCCO2 for the selective synthesis of dimethyl carbonate (DMC) by reaction of CO2 with trimethyl orthoacetate, which also produces methyl acetate (AcOMe) as a byproduct and dimethyl ether as a side product (Scheme 5). A primary incentive of this study was to evaluate the use of SCCO2 as an alternative to phosgene for this reaction. Various metal alkoxides with and without promoters were evaluated as catalytic systems, and the reaction was found to be strongly dependent on the alkox-... 

The synthesis of TDI begins with the nitration of toluene, using a nitric acid-sulfuric acid mixture. The nitration product typically contains at least 75 percent 2,4-dinitrotoluene with the balance mostly 2,6-dinitrotoluene. The nitration product next is catalytically reduced to tolylene diamine. Lastly, the diamine mixture is dissolved in chlorobenzenes and reacted with phosgene to produce the TDI. After phosgenation, the mixture is stripped of the solvent and separated by distillation. The final product is an 80 20 isomer mixture. 

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