Question

How is oxalic acid prepared by:
(i) laboratory method
(ii) Industrially from sodium formate

Answer 1

Hint: Oxalic acid can be prepared by various methods. It can be prepared in a laboratory, can be prepared from propylene, can be industrially prepared from sodium formate, and can be prepared through dimethyl oxalate process.

Complete answer step by step: Oxalic acid is an organic compound with a chemical formula ${C}_{2}{H}_{2}{O}_{4}$. It is a white crystalline solid which forms a colorless solution in water.
Now, let us look at the preparation of oxalic acid:
1. Preparation by laboratory method: It is prepared in the laboratory by oxidizing sucrose with the help of nitric acid in the presence of a small amount catalyst vanadium peroxide. The sugar is placed in the flat-bottomed flask and nitric acid is added to it. Then the flask is heated in a bath of boiling water. Then sugar will dissolve producing an extremely large amount of nitric acid fumes. As soon as this occurs, the flask is removed from the bath and placed on a surface that doesn't conduct heat. After 15 minutes, pour the still-hot solution into an evaporating basin. The solution is evaporated with mild heat from a Bunsen burner for about 15 minutes until it reaches a volume of about 20 mL, then about 40 mL of water is added. The solution is again evaporated down to about 20 mL and thoroughly cooled in an ice-water bath. Then the rapidly forming crystals of oxalic acid are allowed to complete their crystallization in about 10 minutes. The remaining solution is filtered through filter paper, and the crystals are added to a small amount of hot water. Then the oxalic acid is allowed to recrystallize, which takes about 20 minutes. The crystals are dried by pressing them between pads of drying paper or with a desiccator. This preparation should yield about 7 g of oxalic acid. The reaction involved is as follows.
$\underset { Cane\quad Sugar }{ { C }_{ 12 }{ H }_{ 22 }{ O }_{ 11 } } \quad +\quad HN{ O }_{ 3 }\quad \xrightarrow [ { V }_{ 2 }{ O }_{ 5 } ]{ \quad } \quad \underset { Oxalic\quad acid }{ { (COOH) }_{ 2 } } $
2. Preparation industrially by sodium formate: In this method, solid sodium hydroxide and carbon monoxide react together at 2000 degrees Celsius temperature and 150 psi pressure in an autoclave to produce sodium formate. After the completion of the reaction, the pressure in the autoclave is reduced gradually but the temperature is increased to 4000 degrees Celsius. This reaction is completed by ceasing the hydrogen. Then the reaction mixture was collected in a precipitator and calcium hydroxide was added to it with constant stirring. After this, the calcium oxalate formed is filtered and the sodium hydroxide is concentrated so that it can be reused. The filtered calcium oxalate is taken into an acidifier along with a small amount of calcium carbonate and then treated with dilute sulphuric acid. Due to this, the calcium precipitates and as a result, calcium sulphate dihydrate is formed. Then this is taken to a crystallizer and crystals of oxalic acid are formed. The reaction involved is as follows.
$\underset { Sodium\quad formate }{ 2HCOONa } \quad \xrightarrow [ NaOH ]{ \quad } \quad { (COONa) }_{ 2 }\quad \xrightarrow [ Ca{ (OH) }_{ 2 } ]{ \quad } \quad Ca{ (OO) }_{ 2 }\quad \xrightarrow [ { H }_{ 2 }{ XO }_{ 4 } ]{ \quad } \quad \underset { Oxalic\quad Acid }{ { (COOH) }_{ 2 } } $

Note: Do take care while handling oxalic acid as it is toxic due to its acidic and chelating properties. It can cause burns and nausea, vomiting, shock and convulsions. It is specially toxic when ingested.