Dialkyl oxidative carbonylation

Ketene can also be oxidatively carbonylated, using PdC as the catalyst and alkyl nitrites as the oxidant, to give dialkyl malonates (Eq. 26) [125]. Ke-todiesters have been obtained from diketene (Eq. 27) [126]. 

Summarizing the different results from the literature, under the conditions of oxidative carbonylation in the presence of alcohols and catalytic amounts of PdCl2, esters of a,)0-unsaturated carboxylic acids, j0-alkoxy-esters and 2-sub-stituted dialkyl succinates are generally obtained, or mixtures of all of these compounds. Preferably CuCl2, but also other transition metal salts, can be used as co-catalysts (eq. (2)). 

Oxidative Carbonylation of Aliphatic Alcohols Giving Dialkyl Carbonates... 

By oxidative carbonylation of lower aliphatic alcohols in the presence of oxygen or other suitable oxidants dialkyl carbonates and dialkyl oxalates are obtained, depending on the catalyst and the chosen reaction conditions (eqs. (10) and (11)). 

Obviously only dimethyl carbonate is obtained in acceptable selectivities and space-time yields according to this method, although the analogous preparation of higher dialkyl carbonates and simple cyclic carbonates has also been described. Phenols do not give diaryl carbonates by CuCl-catalyzed oxidative carbonylation. 

The preparation of dialkyl oxalates by oxidative carbonylation of alcohols was first described by Fenton et al. in the early 1970s [72-74]. For example, the reaction can be carried out at a temperature around 125 °C and a pressure of about 70 bar in the presence of PdCl2 and iron or copper salts. Water is formed as a by-product and has to be removed from the reaction mixture by the addition of water-binding agents such as trialkyl orthoformates. Instead of oxygen benzo-quinone can also be used for the reoxidation of the catalyst system. Ammonia or amines seem to have a positive influence on selectivity and efficiency of the reae-tion. For some more examples, cf. [77-80, 117]. Mechanistic studies give some indication that alkoxycarbonylpalladium species occur as intermediates [52, 75, 76] (eq. (12)). 

Based on their alkyl nitrite technology, Ube developed their own new proeess for the manufacture of dialkyl oxalates by oxidative carbonylation of alcohols. This process is a two-step reaction, in which alkyl nitrite acts as an reoxidant for the palladium catalyst system, similarly to the situation in the preparation of dialkyl carbonates mentioned above. The published patent literature does not make it possible to give exact details about the Ube industrial plant in Yamaguchi, Japan, which has produced several thousands tons of dibutyl oxalate annually since 1978. The first step of the manufacturing process for dialkyl oxalates is the preparation of the gaseous alkyl nitrite from NO, oxygen, and... 

Palladium catalysts are widely used in liquid phase aerobic oxidations, and numerous examples have been employed for large-scale chemical production (Scheme 8.1). Several industrially important examples are the focus ofdedicated chapters in this book Wacker and Wacker-type oxidation of alkenes into aldehydes, ketones, and acetals (Scheme 8.1a Chapters 9 and 11), 1,4-diacetoxylation of 1,3-butadiene (Scheme 8.1b Chapter 10), and oxidative esterification of methacrolein to methyl methacrylate (Scheme 8.1c Chapter 13). In this introductory chapter, we survey a number of other Pd-catalyzed oxidation reactions that have industrial significance, including acetoxylation of ethylene to vinyl acetate (Scheme 8. Id), oxidative carbonylation of alcohols to dialkyl oxalates and carbonates (Scheme 8.1e), and oxidative coupling of dimethyl phthalate to 3,3, 4,4 -tetramethyl biphenylcarboxy-late (Scheme 8.1f). 

Oxidative carbonylation of alcohols in the presence of CO provides an economically viable route to dialkyl carbonates and/or oxalates (Eqs. (8.4) and (8.5)), both of which have important industrial applications. Dialkyl carbonates (e.g., dimethyl carbonate, propylene carbonate) are excellent solvents for a variety of organic substances [14]. Dialkyl oxalates have utility as solvents, C2 building blocks in fine chemicals synthesis, and intermediates in the manufacture of oxamide (as a fertilizer) [15]. Hydrogenation of dialkyl oxalates provides an alternative route to ethylene glycol that is independent of oil-derived resources [15,16]. 

Dialkyl oxalate esters can be synthesized by oxidative carbonylation catalyzed by palladium complexes with a cocatalyst in the presence of alcohol. The process of... 

Oxidation of oximes to nitro compounds with m-CPBA has been applied to the synthesis of dialkyl 1-nitroalkanephosphonates (Eq. 2.63),124 which are useful reagents for conversion of carbonyl compounds to nitroalkenes.125... 

In the case of acetylenic amides, the carbonyl oxygen atom turned out to be nucleoplilic enough to directly attack the coordinated triple bond, owing to the conjugation with the amide moiety. Thus, cGa-dialkyl substituted 2-ynylamides smoothly underwent oxidative cyclization-alkoxycarbonylation to afford new oxazoline derivatives in good yields (Eq. 44) [102,113]. 

Dialkyl-l,2,4-oxadithiolane-2-5 -oxides (160) have been synthesized from the dihydro thia-diazole (161) via nitrogen extrusion and 1,3-dipolar cycloaddition of the intermediate ylide with sulfur dioxide (Scheme 45) <90BSB265>. The formation and trapping of carbonyl oxides is described... 

Results obtained in glass apparatus are summarized in Figure 1. The unsaturation falls off nearly linearly after a short induction period. After the hydroperoxide functional groups attain their maximum, the olefin disappearance decreases and becomes nonlinear as it is consumed by reaction to form polymeric dialkyl peroxide functions. The maximum concentration of polymeric dialkyl peroxide occurs well after the maximum alkenyl hydroperoxide concentration, giving the appearance of a sequential oxidation mechanism. Infrared and gas-liquid chromatographic analyses showed that hydroxylic derivatives, carbonyl derivatives, and lower molecular weight olefins continued to build up as by-products as the oxidation proceeded, as does the acidity titer. 

The vinyl C with more H s is converted into 0=0. Alkenes can also be transformed into dialkyl carbonyls by a carbonylation-oxidation procedure. 

The carbonyl functionality of MIBK can be hydrogenated over nickel catalysts to yield methyl isobutyl carbinol (4-methyl-2-pentanol or methyl amyl alcohol) [108-11-2]. Industrial processes coproduce methyl isobutyl carbinol during the hydrogenation of mesityl oxide to MIBK. The product ratio of methyl isobutyl carbinol—MIBK during this reaction can be shifted toward methyl isobutyl carbinol by adopting a higher than normal pressure and H2 organic ratio (59). Methyl isobutyl carbinol is used as an ore flotation frother and to produce zinc dialkyl dithiophosphate lube oil additives. It is produced in the United States by Shell and Union Carbide ( 1.12/kg, October 1994). 

In reaction with benzaldehyde or its dimethyl acetal, or benzylidene dibromide, sucrose undergoes conversion into its 4,6-acetal in moderate yield (28-35%).160,161 The transacetalation reaction of dialkyl acetals prepared from unsaturated or aromatic aldehydes can take place under very mild acidic conditions. For example, sucrose-derived monomers or surfactants (variously substituted 4,6-(9-methylidenesucroses) have been prepared146,162 and 4,6-monoacetals incorporating masked aromas or fragrances derived from p-citral or a- or p-ionone were prepared directly from sucrose in high yields.163,164 These latter molecules, whose unsaturated carbonyl system is very susceptible to oxidation, are thus temporarily protected and are readily released under very mild conditions (Scheme 13). 

As expected, the reaction of the lithium salts of phosphonates with oxygen results in the formation of dialkyl phosphoric acids-8 and carbonyl products i.e. the cleavage of the C-P bond takes place (, 5). However, when the halomagnesiurn salts of phosphonates Z were oxidized, a-hydroxyphosphonates 2 were formed. 

Similarly, preparation of a,a-difluorohomoallylic alcohols has been achieved by zinc-mediated addition of CH2=CHCF2Br to carbonyl compounds.29 The reaction is successful with dialkyl ketones as well as aliphatic and aromatic aldehydes (Equation 4.12). The allylation products are particularly useful since the alkene may be oxidized to an aldehyde,32 epoxide,33 or converted to a 8-lactone34 via hydroformylation. 

OXIDATION, REAGENTS Barium mangan-ate. Benzyl(triethyl)ammonium permanganate. Bispyridinesilver permanganate. Bis(trimethylsilyl)peroxide. t-Butyl hydroperoxide. t-Butyl hydroperoxide-Benzyltri-methylammonium tetrabromooxomolyb-dale. t-Butyl hydroperoxide-Bisoxobis-(2,4-pentadionato)molybdenum. t-Butyl hydroperoxide-Chromium carbonyl. t-Bu-tyl hydroperoxide-Dialkyl tartrate-Titan-ium(IV) isopropoxide. t-Butyl hydroper-... 

---