Lithium iodide catalyst

A lower operating P of 10.3 MPa is possible with a rhodium-cobalt-lithium-iodide catalyst. In this case, the chemistry changes to ... 

Lithium Iodide. Lithium iodide [10377-51 -2/, Lil, is the most difficult lithium halide to prepare and has few appHcations. Aqueous solutions of the salt can be prepared by carehil neutralization of hydroiodic acid with lithium carbonate or lithium hydroxide. Concentration of the aqueous solution leads successively to the trihydrate [7790-22-9] dihydrate [17023-25-5] and monohydrate [17023-24 ] which melt congmendy at 75, 79, and 130°C, respectively. The anhydrous salt can be obtained by carehil removal of water under vacuum, but because of the strong tendency to oxidize and eliminate iodine which occurs on heating the salt ia air, it is often prepared from reactions of lithium metal or lithium hydride with iodine ia organic solvents. The salt is extremely soluble ia water (62.6 wt % at 25°C) (59) and the solutions have extremely low vapor pressures (60). Lithium iodide is used as an electrolyte ia selected lithium battery appHcations, where it is formed in situ from reaction of lithium metal with iodine. It can also be a component of low melting molten salts and as a catalyst ia aldol condensations. 

Earlier catalysts were based on cobalt, iron, and nickel. However, recent catalytic systems involve rhodium compounds promoted by methyl iodide and lithium iodide (48,49). Higher mol wt alkyl esters do not show any particular abiUty to undergo carbonylation to anhydrides. 

One approach which enables lower water concentrations to be used for rhodium-catalysed methanol carbonylation is the addition of iodide salts, especially lithium iodide, as exemplified by the Hoechst-Celanese Acid Optimisation (AO) technology [30]. Iodide salt promoters allow carbonylation rates to be achieved at low (< 4 M) [H2O] that are comparable with those in the conventional Monsanto process (where [H20] > 10 M) while maintaining catalyst stability. In the absence of an iodide salt promoter, lowering the water concentration would result in a decrease in the proportion of Rh existing as [Rh(CO)2l2] . However, in the iodide-promoted process, a higher concentration of methyl acetate is also employed, which reacts with the other components as shown in Eqs. 3, 7 and 8 ... 

AO Plus [Acid Optimisation Plus] A process for making acetic acid by carbonylating methanol. Based on the Monsanto Acetic Acid process, but an improved catalyst (rhodium with lithium iodide) permits operation at lower levels of water. Developed by Celanese in the 1980s and operated by that company in Clear Lake, TX. Residual iodide in the product is removed by the Silverguard process. 

The basic organometallic reaction cycle for the Rh/I catalyzed carbonylation of methyl acetate is the same as for methanol carbonylation. However some differences arise due to the absence of water in the anhydrous process. As described in Section 4.2.4, the Monsanto acetic acid process employs quite high water concentrations to maintain catalyst stability and activity, since at low water levels the catalyst tends to convert into an inactive Rh(III) form. An alternative strategy, employed in anhydrous methyl acetate carbonylation, is to use iodide salts as promoters/stabilizers. The Eastman process uses a substantial concentration of lithium iodide, whereas a quaternary ammonium iodide is used by BP in their combined acetic acid/anhydride process. The iodide salt is thought to aid catalysis by acting as an alternative source of iodide (in addition to HI) for activation of the methyl acetate substrate (Equation 17) ... 

DIENES Dichloromalcic anhydride. DITERPENES Palladium catalysts. OLEFINS Cuprous chloride. Lithium di-phenylphosphide. Lithium orthophosphate. Potassium r-butoxide. Thiophe-nol-Azobuty toni tide. OXASPIROPENTANE Lithium iodide. 

The use of aluminium chloride leads to some concomitant cyclobutanone formation, when possible. Lithium iodide and lithium thiocyanate have also been used as catalysts, and in these cases the reaction occurs stereospecifically with net retention of configuration at the migration terminus, presumably via the intermediacy of a lithium 2-iodocyclobu-toxide (equation 170) ... 

The catalysts used are bromine, iodine, haloamides I and/or polymerization inhibitors, in general in amounts of from 0.0001 to 0.1 preferably from 0.001 to 0.05, mole of catalyst per mole of methyi ketone. Instead of the above catalysts, it is also possible to usr compounds which form such catalysts under the reaction conditions, e.g to use bromides and iodides in place of bromine or iodine. Water-soluble halides are preferred and are advantageously used in the form of thei alkaline earth metal salts or, especially, their alkali metal salts, e.g calcium bromide, calcium iodide, magnesium bromide, magnesiais iodide, lithium bromide, lithium iodide and especially sodium bromide or iodide or potassium bromide or iodide... 

In the low-water AO technology [23], the major function of the iodide salts is to stabilize the rhodium carbonyl catalyst complexes from precipitation as insoluble rhodium triiodide (RhD [5c]. Lithium iodide (Lil) is the preferred salt. The iodide salts also promote catalyst activity (see below). However, the key factor that con-... 

The carbonylation process incorporates a rhodium salt, lithium iodide, and methyl iodide as primary catalyst components [80]. The active catalyst form is maintained by the lithium iodide promoter and hydrogen in the carbon monoxide feed to the reaction system. Preferred reaction conditions are a temperature of nearly 190 °C and a pressure of 5 MPa H2/CO. The conversion of methyl acetate to acetic anhydride per passage of reactor is between 50 and 75 %. 

Further development of iridium-complex catalysts was initiated by BP Chemicals in the 1990s, with the hope of identifying reaction conditions under which high activity and selectivity could be achieved. An additional aim was to develop a catalyst that is more robust in the presence of low water concentrations than the rhodium complex catalyst thus, some similarity to the Celanese lithium-iodide stabilized rhodium catalyst was sought. A series of patents provide detail of the discovery by BP of promoters that enhance the activity of an iridium/iodide carbonylation catalyst and, crucially, attain optimum rate at relatively low water concentrations, as illustrated in Figure 2 [116-119]. 

McKervey and coworkers have used lithium iodide as a catalyst for mixed aldol reactions several examples are shown in equation (60). In all cases studied, 2-butanone reacts solely at C-1. The process is also applicable to other ketones, but they react much more slowly than do methyl ketones. For... 

This reaction is carried out over rhodium carbonyls as catalyst using HI as a promoter. Acetic anhydride is produced from the carbonylation of methylacetate over lithium-iodide-promoted rhodium catalyst ... 

SUylation with HMDS is most commonly carried out with acid catalysis. The addition of substoichiometric amounts of chlorotrimethylsilane (TMSCl) to the reaction mixtures has been found to be a convenient method for catalysis of the silylation reaction. The catalyticaUy active species is presumed to be hydrogen chloride, which is liberated upon reaction of the chlorosi-lane with the substrate. Alternatively, protic salts such as ammonium sulfate can be employed as the catalyst. Addition of cat-al)Tic lithium iodide in combination with TMSCl leads to even greater reaction rates. Anilines can be monosilylated by heating with excess HMDS (3 equiv) and catalytic TMSCl and catalytic Lil (eq 2). Silylation occurs without added Lil however, the reaction is much faster in the presence of iodide, presumably due to the in situ formation of a catalytic amount of the more reactive iodotrimethylsilane. 

Pierre and Handel have studied the effect of [2.1.1]-cryptate on the lithium aluminum hydride reduction of cyclohexanone in diglyme [16]. The [2.1.1]-cryptate strongly complexes lithium ion and if sufficient cryptate is used to sequester all of the lithium ion, no reduction occurs. Apparently, lithium ion is needed as an electrophilic catalyst for the reduction to occur (see Eq. 12.8). Consistent with this interpretation is the observation that even in the presence of cryptate, reduction will occur if an excess of lithium iodide is also present. The relatively low reactivity of tetrabutyl-ammonium borohydride in benzene solution may also reflect this property, at least in part [9]. Likewise, the jS-hydroxyethyl quaternary ammonium ions may be better catalysts than non-oxygenated quaternary ions because the hydroxyl may hydrogen bond to carbonyl and provide electrophilic catalysis [5]. Similar, though less dramatic results, have been observed in the reduction of aromatic aldehydes and ketones by lithium aluminum hydride in the presence of [2.1.1]-cryptate [17]. 

The presence of a cation is also important in the lithium aluminum hydride reduction of cyclohexanone [12, 13]. Lithium ion is apparently required as an electrophilic catalyst for the reduction of cyclohexanone and if an appropriately sized cryptate is added to the reducing medium, a retardation of the reduction is observed. Addition of [2.1.1]-cryptate to the reduction system in quantities sufficient to complex all of the available lithium ion leads to a total absence of reduction. An excess of lithium iodide, however, restores reactivity. This reaction is discussed in Sect. 12.5. 

Solid state primary batteries can provide very long-life operation at low currents. The first example of such an application is the lithium-iodide solid state battery for cardiac pacemakers which is manufactured in the US by Catalyst Research Co., by Wilson Greatbatch, and by Medtronic Inc. The second example is lithium-glass battery, whose application envisaged is mainly as a power source for electronic computers, such as C-MOS memory backup. Cells commercially available are design XR2025HT by the Union Carbide group. 

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