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• Chemical Properties

  Cyclopropane is the simplest possible cyclical hydrocarbon. Though saturated, its cyclical structure endows it with some of the properties associated with unsaturated compounds. It is relatively stable chemically, does not isomerize or polymerize during prolonged storage under normal conditions, and does not react with soda lime in the presence of heat. The gas is colourless, sweet smelling and, in concentrations in excess of 50 percent, is slightly irritant to respiratory mucosa. The molecular weight of the gas is 42.08 and the vapour density (air=1.0) is 1-75 at 20°C (Macintosh, Mushin and Epstein, 1963). The boiling point of liquid cyclopropane is -33°C at a pressure of 760 Torr, and the critical temperature is 125°C. The critical pressure is 54 atmospheres, but at room temperature the gas liquefies when exposed to pressures of 5 lb./sq.in.
  
  As supplied, the gas is 99.5 percent or more pure, but possible impurities include propylene, allene, cyclohexane, nitrogen, carbon dioxide, and bromor chloropropane. Propylene is the most important contaminant, up to 1 per cent being acceptable, but concentrations over 3 per cent are toxic. ;

• History

  Cyclopropane was discovered by Freund (1882), but the anaesthetic properties of hydrocarbons with the general formula CnH2n were appreciated earlier. John Snow (1858), for example, administered amylene (C5H10) to 238 patients. In 1923, ethylene (C2H4) was introduced into clinical anaesthesia, but its low potency and inflammability restricted its use. At the University of Toronto, research by G. H. W. Lucas and V. E. Henderson on propylene (CH3.CH:CH2) revealed certain samples to show marked cardiac toxicity. Lucas suggested that the toxicity might arise from one of the impurities present in the samples, the cyclic isomer of propylene, cyclopropane. Pure samples of cyclopropane were prepared and this, when tested by Lucas and Henderson, proved to be a more potent and suitable anaesthetic agent than propylene. ;

• Solubility constants

  Cyclopropane is sparingly soluble in water, but strongly lipophilic. This is shown by a water/gas partition coefficient of 0-204 (Orcutt and Seevers, 1937) and an oil/gas coefficient of 11-2 (Blumberg et al., 1952). The strong lipoid and protein afiBnities of the gas lead not only to the carriage of 2-5 times more cyclopropane by red cells than plasma, but also to a blood/gas partition coefficient which varies with both the haemoglobin concentration and the plasma fat content of blood (Robbins, 1958). The Ostwald solubility coefficient for cyclopropane and whole blood at 37℃, and with 15g Hb per 100 ml, is 0-415 (Posati and Faulconer, 1958).

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• Uses

  Cyclopropane is a powerful, nonirritating agent which can produce anaesthesia in a few breaths. It has been used used as an anesthetic, but this use has been discontinued because the gas is dangerous to manufacture and handle.
  Cyclopropane has been used as the pseudo-π unsaturated hydrocarbon prototype to study the rotational spectrum of its complex formed with chlorine monofluoride and the similarity of this complex with isotopomers. ;

• Reactions

  Cyclopropane and cyclobutane are gases at ordinary temperatures; the remaining cycloalkanes are liquids. Their melting points and boiling points show a gradual rise with the increase in molecular weight.
  Addition of Cl2 and Br2: Cydopropane reacts with Cl, and Br, at room temperature and in the absence of diffused sunlight to produce 1,3- dichlorocyclopropane and 1,3-dibromocyclopropane respective.
  Cyclopropane reacts with HBr and HI to give 1-bromopropane and 1-iodopropane.
  
  Cyclopropane and cyclobutane react with hydrogen in the presence of a nickel catalyst to produce propane and n-butane respectively. ;

• Preparation

  Stroll quantities of cyclopropane have been prepared from natural deposits of the gas in the United States, but current practice involves the reaction of trimethylene glycol with hydrobromic acid to form1,3-Dibromopropane. The latter compound, in the presence of zinc dust, converts to the cyclic compound, cyclopropane.;

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