5-Sulphosalicylic acid

5-Sulphosalicylic acid is an organic compound possessing both sulphonic and carboxylic acid functional groups. It's used in integral colour anodizing, however its main use is as a reagent to measure protein levels in urine. Under standard conditions, 5-sulphosalicylic acid exists as a white crystalline solid.

5-sulphosalicylic acid is easily prepared by the sulphonation of salicylic acid with concentrated sulphuric acid. I decided to try this synthesis out.

To a 500ml round bottom flask, I added 3.71g of salicylic acid. I carefully added 18ml of 98% sulphuric acid and stirred to thoroughly mix the two chemicals. I then set the flask up for reflux with a Liebig condenser. I refluxed the mixture for 1 hour and 30 minutes using a boiling water bath as the heat source. After a few minutes of reflux, the suspended salicylic acid dissolved, giving a blood-red liquid, which gradually turned brown. Once the reflux was complete, I allowed the mixture to cool to room temperature. A small amount of solid material separated. I then, very slowly and with rapid stirring, poured the mixture (including the solid material) into a 250ml beaker containing 140ml of saturated sodium chloride solution. Initially not much seemed to happen, but after a few seconds, a fine white precipitate formed. This is the product, 5-sulphosalicylic acid dihydrate.

I filtered the 5-sulphosalicylic acid off, washing it on the filter with two 15ml portions of cold water. I then dried the 5-sulposalicylic acid. This product however did not seem to be very pure at all, so I recrystallized the 5-sulphosalicylic acid from saturated sodium chloride solution. After recrystallization, I was left with 3.68g of fairly pure 5-sulphosalicylic acid dihydrate as a fine white crystalline powder. This represents a 54% yield.

C6H4(OH)COOH + H2SO4 ==> C6H3HSO3(OH)COOH + H2O

Copper metal, two ways

Copper is possibly the oldest metal known to mankind. It was the first metal cast into a shape and even the first to be smelted from ore. I thought it might be interesting to try some different approaches to making copper metal from its compounds. There are many ways it can be done, and in this post I present two methods that I investigated.

The first involves the displacement reaction between magnesium and copper(ii) sulphate.

To a 150ml beaker, I added 11.55g of copper(ii) sulphate pentahydrate and 50ml of water. With a bit of swirling, the copper sulphate dissolved, giving a nice blue-coloured solution. I then added in 1.07g of powdered magnesium metal in portions, over the course of about 2 minutes. A vigorous and exothermic reaction immediately began. The mixture started bubbling, giving off steam and releasing a large amount of heat. Gradually, the mixture turned a mud-green colour, which became a brown and finally an orange-brown. At this point it became evident that the colour was caused by small particles of copper metal in suspension. Once all the magnesium had been added, I left the mixture to stand until all the orange-brown copper particles had settled to the bottom of the beaker. I then decanted as much of the liquid off as possible without losing any copper. To the residual copper and liquid that was left, I added 50ml of 5% acetic acid.

I gave the mixture a stir, then left it to stand for about 10 minutes. Then I filtered the mixture, washing the copper on the filter with two 50ml portions of water. And finally I dried the copper powder. 1.95g of copper powder was collected, corresponding to a 70% yield.

The other method I investigated was a thermite reaction between copper(ii) oxide and magnesium.

3.77g of copper(ii) oxide and 1.15g of powdered magnesium metal were added to a mortar and pestle and ground into a fine powder. The powder was then spread on a brick and ignited with a butane torch. A violent thermite reaction began, giving off large amounts of fire and smoke. Once the reaction was complete, I collected the residue and added it to a 250ml beaker. I then added 30ml of 16.5% hydrochloric acid to the beaker and swirled this for a few minutes. I filtered the mixture and transferred the copper on the filter back to the 250ml beaker. I added an additional 30ml of 16.5% hydrochloric acid, stirred the mixture for a few minutes, then filtered off the copper, and washed it on the filter with 50ml of water. After drying, this gave 0.09g of very dirty copper metal, which represents a miserable 3% yield.

Left = copper made by the first method    Right = Copper(ii) oxide thermite from the second method

CuSO4 + Mg ==> MgSO4 + Cu  /  CuO + Mg ==> MgO + Cu

2 CH3COOH + Mg ==> Mg(CH3COO)2 + H2  /  2 HCl + CuO ==> CuCl2 + H2O

2 HCl + MgO ==> MgCl2 + H2O  /  2 HCl + Mg ==> MgCl2 + H2