1. Carbon monoxide and sodium hydroxide react at 160 and 2MPa to produce sodium formate. Then sodium oxalate is obtained by dehydrogenating sodium formate at 400 C.

2. Take 212 g sodium carbonate and heat it to dissolve in 1L water, then add a small amount of oxalic acid water solution to the water solution. At this time, the impurities in the water can be removed by co-precipitation with sodium oxalate while the precipitation of sodium oxalate is formed. Then take 252g refined oxalic acid and dissolve it in 1L hot water (90 C). In beaker, 500 mL of water is heated to 90 C in advance. Under stirring, the volume of oxalic acid and sodium carbonate solution is dripped slowly into beaker with a separating funnel. The pH value of the solution should be kept between 6 and 7 in this process. After dropping and heating a little, the solution is cooled and filtered to form crystals. The crystals are washed with cold water and dried at 240-250 C. and then placed in a desiccator of concentrated sulfuric acid. Sodium oxalate can be purified by water recrystallization. First, it is dissolved in hot water and saturated at about 90 C. Then, 75% ethanol water solution is added to the filtrate, cooled, filtered out and dried at 250 C. Because the sodium oxalate aqueous solution can react with glassware, and because the raw material contains impurities, the product contains silicon dichloride and sodium carbonate. It is suggested that the preparation of sodium oxalate should be operated as soon as possible, and the refined sodium hydroxide can be used instead of sodium carbonate. In addition, in the preparation of sodium oxalate, if the solution is acidic, a small amount of sodium oxalate will be produced and precipitated with sodium oxalate. If the product is dried at 250-300 C, sodium oxalate can be decomposed into sodium carbonate by thermal decomposition.

3. Dissolve oxalic acid dihydrate in water, heat it, add sodium hydroxide solution drop by drop to precipitate sodium oxalate crystallization, then wash it with water and anhydrous ethanol, and dry it to get pure sodium oxalate.

4. The sodium hydroxide solution is slowly added to the oxalic acid solution at 70-80 ~C under continuous stirring until the phenolphthalein reacts strongly alkaline and keeps the temperature unchanged. After the reaction is over, the sodium oxalate crystals are quickly filtered out. After the water is washed up to the PH value, the sodium oxalate crystals are washed with a small amount of ethanol and strongly sucked and filtered, and then dried at 150-200 ~C under constant stirring.