Lithium oxalate, decomposition

These salts decompose [39] to the carbonates in the temperature intervals Li, 811-826 K Na, 737-814 K and K, 754-798 K (from DTA measurements, 5 K min-1). The reaction of lithium oxalate [98] (742— 765 K) obeyed the contracting volume equation [eqn. (7), n = 3] with E = 223 13 kJ mole-1. A marked increase in surface area during the initial stages of decomposition was later followed by extensive sintering. 

Decomposition of lithium oxalate [84] (742 to 765 K) yielded the carbonate and was accompanied by an initial large increase in surface area, followed by extensive sintering. The nr-time curve was sigmoid with no induction period and = 223 kJ... 

During a synthesis of the Chlorothricolide, Roush and Sciotti encountered unexpected problems with the hydrolysis of the dimethyl acetal 54.1 [Scheme 2.54].112 Use of some of the standard hydrolysis conditions (oxalic acid, PPTS, PTSA, HO Ac, or trifluoroacetic acid — all in acetone) resulted in recovery of 54.1 or decomposition. Success was achieved by exploiting the mild Lewis acidic properties of the lithium cation under conditions first reported by Lipshutz and Harvey.113 Thus treatment of the dimethyl acetal 54,1 with lithium tetrafluoroborate in acetonitrile containing 2% water returned the desired aldehyde 54J in 97% yield after 2 h at room temperature. The reaction was also applied to the deprotection of a cyclic ketal in a synthesis of Pumi-liotoxin.114 115... 

Non-isothermal kinetic studies [69] of the decomposition of samples of nickel oxalate dihydrate doped with Li and Cr showed no regular pattern of behaviour in the values of the Arrhenius parameters reported for the dehydration. There was evidence that lithium promoted the subsequent decomposition step, but no description of the role of the additive was given. 

Hofmann (53) found an appreciable amount of formaldehyde (about 25%) and small amounts of methyl formate during the decomposition of zinc formate. Lithium formate produced acetone (about 20%) from lead formate, formaldehyde and methyl alcohol were formed. Pichler (127) found that during the decomposition of calcium formate, oxalate was formed. In general it appeared that the nature and the amount of the organic by-products depended largely on the reaction conditions [Hofmann (53)]. 

Three detailed applications of thermogravimetry are described with more quantitative interpretations, i.e., efforts are made to develop information on the kinetics and equilibrium. The calcium oxalate/carbonate decomposition is treated first. The lithium hydrogen phosphate polymerization has been discussed above as a step-reaction in Sect. 3.1 (Figs. 3.16-22). Finally, the method and some examples of lifetime determinations based on TGA are shown at the end of this section. 

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