Ammonia:

Ammonia (molecular weight 17) is one of the oldest refrigerants and this was normally working in places where toxicity effects were of secondary significance. Its advantages are its low specific volume, low cost, high COP (of the order of 4.0) and high refrigeration effect per unit mass of the refrigerant. Its chief drawback is its toxicity that prevents its use in air- conditioning & food preservation systems. Ammonia contain a boiling point of -33 ⁰C at atmospheric pressure.