Iodide, carbonyl

Carbonylation of 1,4-dacetoxy butane Rh-carbonyl iodide complex Adipic acid Specialty chemicals... 

Group VIA (Cr, Mo, W). y-Radiolysis studies have been carried out for the simple hexacarbonyls (31,32) and for certain carbonyl iodides (33) and cyclopentadienyl carbonyl iodides (34). In the case of the hexacarbonyls (31,32), two free-radical products have been detected and characterized for Cr(C0)6, weak unidentified EPR signals have been observed for Mo(C0)6, but irradiated W(C0)6 apparently contains no detectable paramagnetic centres. 

Evidence has been presented that iodide salts can promote the oxidative addition of Mel to [Rh(CO)2l2]"> the rate-determining step in the Rh cycle [12]. The precise mechanism of this promotion remains unclear formation of a highly nucleophilic dianion, [Rh(CO)2l3]2 , has been suggested, although there is no direct spectroscopic evidence for its detection. Possible participation of this dianion has been considered in a theoretical study [23]. An alternative nucleophilic dianion, [Rh(CO)2l2(OAc)]2 , has also been proposed [31,32] on the basis that acetate salts (either added or generated in situ via Eq. 7) can promote carbonylation. Iodide salts have also been found to be effective promoters for the anhydrous carbonylation of methyl acetate to acetic anhydride [33]. In the absence of water, the catalyst cannot be maintained in its active form ([Rh(CO)2l2]") by addition of Lil alone, and some H2 is added to the gas feed to reduce the inactive [Rh(CO)2l4]. ... 

In Rh catalysed MeOH carbonylation, the water gas shift reaction is catalysed by Rh carbonyl iodides and the presence of HI. It leads to a loss of yield with respect to CO, both because it is being consumed by the water gas shift and because some CO has to be vented along with H2 and CO2 to prevent them building up in the reactor. In this regime, the trend is for the water gas shift rate to increase relative to the carbonylation rate as [MeOAc] and [H2O] decrease. The presence of H2 tends also to be associated with the formation of small amounts of EtCOOH, which may be sufficient to require separation (Eq. (5)). 

The carbonylation of MeOH catalysed by Ir and Mel can also be operated at lower reactor ]H20] and higher ]MeOAc] than the original Monsanto process and without issues of catalyst stability. Commercially acceptable rates can be achieved at lower ]MeI] concentrations by using promoters such as carbonyl iodide complexes of Ru and Os or covalent iodides such as Inij or Znl2 ]9]. Ionic iodide salts are potent poisons for the Ir catalysed reaction ]11]. In contrast with the Rh catalysed systems, CH4 and not H2 is co-produced as a gaseous by-product (Eq. (8)). 

Many other modifications, particularly of the Rh and Mel catalysed carbonylation of MeOH, have been proposed and some of these have been operated commercially or may have been tested at significant pilot plant scale. These include, for example, the use of phosphine oxide species such as PPh30 [20] as promoters and systems involving immobilizing the Rh on ion exchange resins [21]. Numerous examples of ligand modified catalysts have been described, particularly for Rh, though relatively few complexes have been shown to have any extended lifetime at typical process conditions and none are reported in commercial use [22, 23]. The carbonyl iodides of Ru and Os mentioned above in the context of the Cativa process are also promoters for Rh catalysed carbonylation of MeOH to AcOH [24]. 

Fortunately, the mid-IR stretches of the terminal carbonyls of simple carbonyl iodide complexes of Rh and Ir occur in the region 1950 to 2150 cm Their extinction coefficients are sufficiently strong that even in aqueous AcOH, which would not be a solvent of choice for mid-IR spectroscopy, at concentrations in the range of 100s of ppm w/w, the simple Rh or Ir carbonyl iodides can be detected by FTIR with a modest acquisition time. Indeed much of the original IR work to study both Rh and Ir catalysed carbonylation by workers at Monsanto [11, 25] and by Schrod et al. [26] appears to have been carried out using continuous wavelength machines. 

Neutral Ru carbonyl iodide complexes such as [Ru(CO)4l2] and [Ru(CO)3l2]2, capable of r abstraction, promoted the migratory carbonylation of [IrMe(CO)2l3] in PhCl in a similar way to Inl3, while ionic species such as [Ru(CO)3l3] were inactive. Reactions followed quantitatively by IR showed the molar activity of these Ru species to be similar to that of Inl3. Whereas the stoichiometric reaction of [IrMe(CO)2l3] with Inis could be used preparatively, the reaction with neutral Ru complexes appeared to give rise to Ir-Ru species (Eq. (30)). 

The C-MeOAc/Mel exchange reaction has also been used to probe the interaction of Ru carbonyl iodides with MeOH carbonylation systems. In parallel NMR was used to identify the Ru species present as a function of [H2O] and CO pressure [18]. 

When Ru carbonyl iodides are used as promoters for Ir catalysed carbonylation of MeOH to AcOH, the accurate quantification of Ir species becomes more difficult because the bands of the Ru species overlap those of the Ir species and they have larger extinction coefficients, so dominating the spectra. In batch reactions followed by HP IR, the Ru bands present initially before Ir is added and carbonylation commences have been assigned to neutral Ru carbonyl iodides and [Ru(CO)3l3] ... 

Inl3, which has a similar promotional effect to Ru carbonyl iodides for Ir catalysed MeOH carbonylation to AcOH, of course has no carbonyl bands to obscure the Ir species. Both [Ir(CO)2l4] and [IrMe(CO)2l3] are observed under carbonylation conditions by HP IR, as in the absence of Inl3 [18]. 

Chemical and Catalytic Properties of Ruthenium Carbonyl Iodide Systems during Reactions on Oxygenated Substrates... 

Scheme 1 Lewis acid assisted evolution of alkyl and acyl ruthenium carbonyl iodide intermediates.

These results also demonstrate the ability of the ruthenium carbonyl iodide systems to activate both the alkyl and the acyl part of the formates. The same is true for esters of higher carboxylic acids where new esters of higher homologous acids and alcohols are produced. 

Hieber and Heusinger (3) reported an interesting reaction in which a liquid ammonia solution of ruthenium carbonyl iodide decomposed above — 30 °C to produce free and coordinated formamide ... 

Two homogeneous metal complex water-gas shift catalyst systems have recently appeared 98, 99). The more active of these comes from our Rochester laboratory (99, 99a). It is composed of rhodium carbonyl iodide under CO in an acetic acid solution of hydriodic acid and water. The catalyst system is active at less than 95°C and less than 1 atm CO pressure. Catalysis of the water-gas shift reaction has been unequivocally established by monitoring the CO reactant and the H2 and C02 products by gas chromatography The amount of CO consumed matches closely with the amounts of H2 and C02 product evolved throughout the reaction (99). Mass spectrometry confirms the identity of the C02 and H2 products. The reaction conditions have not yet been optimized, but efficiencies of 9 cycles/day have been recorded at 90°C under 0.5 atm of CO. Appropriate control experiments have been carried out, and have established the necessity of both strong acid and iodide. In addition, a reaction carried out with labeled 13CO yielded the same amount of label in the C02 product, ruling out any possible contribution of acetic acid decomposition to C02 production (99). 

A group at Monsanto has also studied the catalysis of the water-gas shift reaction by rhodium carbonyl iodide (103b). The main difference between their work and our own is the choice of reaction conditions. Their study was conducted at 185°C under 200-400 psig carbon monoxide. Despite this drastic difference in reaction conditions, the studies are surprisingly consistent. In particular, the Monsanto group also finds evidence for two rate-limiting reactions. They did not find this by temperature variation, but instead, consistent with our own work, find that at low acid and iodide... 

The thermochemical aspects of these reactions have been discussed in terms of heats of formation of the halides of elements of the iron group, and of the acceptor metal (75). The yield of carbonyls was especially favored with the iodides and also with sulfides or sulfur-containing materials (76). With iron and cobalt iodides the reaction is facilitated by formation of the carbonyl iodide as an intermediate. 

Two carbonyl complexes K2[Ru(CN)2I2(CO)2] (from ruthenium carbonyl iodide and KCN)4 and [RuC1(CN)(NH3)(CO)(PPh3)2] (4) (from treatment of [RuCl2(CCl2)(CO)(PPh3)2] with ammonia) are known. Reaction of the latter with CO gives [RuCl(CN)(CO)2(PPh3)2] (5).49... 

Acetica A process for making acetic acid by the heterogeneous carbonylation of methanol in a bubble column reactor. The catalyst is a rhodium carbonyl iodide, anchored by ion-pairing to a polyvinyl pyridine resin. Developed by Chiyoda Corporation and UOP and first described in 1998. Licensed to Guizhou Crystal Organic Chemical Group, China, in 2002 one plant was under construction in 2005. 

The carbonyl iodides of Rh1 and Rhm play an important role in the carbonylation of CH3OH to CH3CO2H (see Chapter 21) in which Lil and the rhodium species are involved in a rather complex catalytic cycle.3... 

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