Diethyl-ether

The ignition di am for diethyl ether—oxygen mixtures has been determined [68] and the slow combustion has been studied in some detail. The low temperature oxidation becomes appreciable at 120 °C and Lemay and Ouellet [69], working at 160—175 °C which was below the lower limit of cool flame for in their pyrex reaction vessel, observed an initial pressure drop during which oxygen was consumed by a zero-order process with an activation energy of about 50 kcal. mole. Peroxides 

The apparent activation energy between 150 and 190 °C, the temperature at which cool flames appear, was about 23 kcal.mole for a mixture of 100 torr diethyl ether and 50 torr oxygen. Packii the reaction vessel with lengths of pyrex tubing slightly increased the induction period and lowered the rate to about 2/3 of its value in an empty vessel. 

While the order of reaction with respect to ether was about unity, excess oxygen tended to decrease the rate and to lengthen the induction period. This behaviour is in marked contrast to that commonly observed in hydrocarbon qombustion. 

A mechanism was proposed by Waddington [70] which involved formation of peracetic acid from acetaldehyde, itself a breakdown product of the radical formed by attack of oxygen on the fuel, viz. 

CH3CHO + Oj = CH3COOOH Chain branching was due to breakdown of the peracid 

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The covalently bonded oxygen atom still has two lone pairs of electrons and can act as an electron pair donor. It rarely donates both pairs (to achieve 4-coordination) and usually only one donor bond is formed. A water molecule, for example, can donate to a proton, forming H30, and diethyl ether can donate to an acceptor such as boron trifluoride ... 

If the mixture contains an excess of ethanol, and is heated to 140°, the ethyl hydrogen sulphate reacts with the ethanol, giving diethyl ether And regenerating the sulphuric acid ... 

Diethyl ether is a mobile, colourless liquid having b.p. 35° and dy 0720. It has a characteristic odour, and a burning taste. It is used chiefly as a solvent, and was formerly widely used as an anaesthetic owing to its chemical non-reactivity, it is very seldom used actually as a reagent, except in the preparation of Grignard reagents (p. 280) where probably its chemical properties reinforce its solvent action. 

Ethyl bromide is a colourless liquid, of b.p. 38° and [Pg.102]

Ethers. Diethyl ether, di-n-propyl ether, di-isopropyl ether, ani ... 

Diethyl ether, b.p. 35 . Di n-propyl ether, b.p. 90. Di propyl ether, b.p. 67 5. Anxsole methyl phenyl ether), b.p. 154 . Phenetole (ethyl... 

Iodine solutions. Dissolve i crystal of iodine in diethyl ether and note the brown colour. Aromatic hydrocarbons e.g. benzene) give purple solutions. 

Ester formation. Heat under very efficient reflux 1 ml. of diethyl ether, 4 ml. of glacial acetic acid and i ml. of cone. H2SO4 for ro minutes. Distil off 2 ml. of liquid. Use a few drops of this liquid for the hydroxamic add test for esters (p. 334). Use the remainder for other tests for esters (p. 354). 

Heat together under very efficient water reflux 1 g. of freshly fused dry powdered ZnClg, 2 ml. of diethyl ether and 0 5 g. of 3,5 -dinitrobenzoyl chloride for 2 hours. Shake the product with 5 ml. of water and ther add 10% NaOH solution until all the ZnCl, and excess of 3,5-dinitro> benzoyl chloride and 3,5-dinitrobenzoic acid have gone into solution. Filter at the pump and recrystallise from petroleum (b.p. 40-60°) to obtain ethyl 3,5-dinitrobenzoate, m.p. 93°. (M ps. of other 3,5 dinitro-benzoates, p. 536.)... 

Many pairs of partially miscible liquids possess neither a lower nor an upper C.S.T. for reasons outlined in the previous paragraph. Thus consider the two liquid phases from the two components water and diethyl ether. Upon cooling the system at constant pressure, a point will be reached when a third phase, ice, will form, thus rendering the production of a lower C.S.T. impossible, likewise, if the temperature of the two layers is raised, the critical point for the ether rich layer will be reached while the two liquid phases have different compositions. Above the critical point the ether-rich layer will be converted into vapour, and hence the system will be convert into a water rich liquid and an ether rich vapour the upper C.S.T. cannot therefore be attained. 

The inflammable solvents most frequently used for reaction media, extraction or recrystallisation are diethyl ether, petroleum ether (b.p. 40-60° and higher ranges), carbon disulphide, acetone, methyl and ethyl alcohols, di-Mo-propyl ether, benzene, and toluene. Special precautions must be taken in handling these (and other equivalent) solvents if the danger of Are is to be more or less completely eliminated. It is advisable to have, if possible, a special bench in the laboratory devoted entirely to the recovery or distillation of these solvents no flames are permitted on this bench. 

Ether. The most satisfactory method for the removal of (diethyl) ether is either on a steam bath fed from an external steam supply or by means of an electrically-heated, constant-level water bath (Fig. 77, 5, 1). If neither of these is available, a water bath containing hot water may be used. The hot water should be brought from another part of the laboratory under no circumstances should there be a free flame under the water bath. It caimot be too strongly emphasised that no flame whatsoever may be present in the vicinity of the distillation apparatus a flame 10 feet away may ignite diethyl ether if a continuous bench top lies between the flame and the still and a gentle draught happens to be blowing in the direction of the flame. 

Diethyl ether will be abbreviated throughout the book to ether. The ether should be reasonably free from peroxides, see Section 11,47,1. 

Absolute diethyl ether. The chief impurities in commercial ether (sp. gr. 0- 720) are water, ethyl alcohol, and, in samples which have been exposed to the air and light for some time, ethyl peroxide. The presence of peroxides may be detected either by the liberation of iodine (brown colouration or blue colouration with starch solution) when a small sample is shaken with an equal volume of 2 per cent, potassium iodide solution and a few drops of dilute hydrochloric acid, or by carrying out the perchromio acid test of inorganic analysis with potassium dichromate solution acidified with dilute sulphuric acid. The peroxides may be removed by shaking with a concentrated solution of a ferrous salt, say, 6-10 g. of ferrous salt (s 10-20 ml. of the prepared concentrated solution) to 1 litre of ether. The concentrated solution of ferrous salt is prepared either from 60 g. of crystallised ferrous sulphate, 6 ml. of concentrated sulphuric acid and 110 ml. of water or from 100 g. of crystallised ferrous chloride, 42 ml. of concentrated hydiochloric acid and 85 ml. of water. Peroxides may also be removed by shaking with an aqueous solution of sodium sulphite (for the removal with stannous chloride, see Section VI,12). 

Di-teo-propyl ether. The commercial product usually contains appreciable quantities of peroxides these should be removed by treatment with an acidified solution of a ferrous salt or with a solution of sodium sulphite (see under Diethyl ether). The ether is then dried with anhydrous calcium chloride and distilled. Pure di-iao-propyl ether has b.p. 68-5°/760 mm. 

Di-alkyl ethers of ethylene glycol, ROCHjCHjOR. The dimethyl ether, b.p. 85°/760 mm., is miscible with water, is a good solvent for organic compounds, and is an excellent inert reaction medium. The diethyl ether (diethyl cdloaolve), b.p. 121-57760 mm., is partially miscible with water (21 per cent, at 20°). 

The diethyl ether of diethylene glycol (diethyl carbitol), b.p. 186°/ 760 mm., is completely miscible with water. The above three ethers may be purified by distillation from sodium. 

Benzene. The analytical reagent grade benzene is satisfactory for most purposes if required dry, it is first treated with anhydrous calcium chloride, filtered, and then placed over sodium wire (for experimental details, see under Diethyl ether, 1). 

Methylene chloride is a useful substitute for diethyl ether when it is desired to employ a solvent which is heavier than water. 

Diethyl ether may be prepared from ethyl alcohol by the sulphuric acid process. A mixture of alcohol and sulphuric acid in equimolecular proportions is heated to about 140° and alcohol is run in at the rate at which the ether produced distils from the reaction mixture. Ethyl hydrogen sulphate (or ethyl sulphuric acid) is first formed and this yields ether either by reacting directly with a molecule of alcohol or by the formation and alcoholysis of diethyl sulphate (I) ... 

The preparation of anhydrous diethyl ether (suitable for Grignard reactions, etc.) is described in Section 11,47,1. The precautions required in handling ether are given in Seetion 11,14. 

The preparation of diethyl ether is described here for the sake of completeness. It is an unsuitable exercise for beginners. Di-n-butyl ether (Section 111,57) offers an excellent alternative. 

CAUTION. Ethers that have been stored for long periods, particularly in partly-filled bottles, frequently contain small quantities of highly explosive peroxides. The presence of peroxides may be detected either by the per-chromic acid test of qualitative inorganic analysis (addition of an acidified solution of potassium dichromate) or by the liberation of iodine from acidified potassium iodide solution (compare Section 11,47,7). The peroxides are nonvolatile and may accumulate in the flask during the distillation of the ether the residue is explosive and may detonate, when distilled, with sufficient violence to shatter the apparatus and cause serious personal injury. If peroxides are found, they must first be removed by treatment with acidified ferrous sulphate solution (Section 11,47,7) or with sodium sulphite solution or with stannous chloride solution (Section VI, 12). The common extraction solvents diethyl ether and di-tso-propyl ether are particularly prone to the formation of peroxides. 

Petroleum ether is preferable to diethyl ether because it removes very little acetic acid from the aqueous phase. 

Peroxide-free ether should be employed for detection and removal of peroxides in diethyl ether, see Section 11,47,i. 

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