Peroxides, detection removal

ChemZtg 51, 981-83(1927) CA 22, 869(1928) (Expln of Ether contg Peroxide detection removal of peroxide) 3) R. Robertson,... 

Ethyl ether [60-29-7] M 74.1, b 34.6 /760mm, d 0.714, n s 1.3555, n 1.35272. Usual impurities are water, EtOH, diethyl peroxide (which is explosive when concentrated), and aldehydes. Peroxides [detected by liberation of iodine from weakly acid (HCl) solutions of KI, or by the blue colour in the ether layer when Img of Na2Cr2O7 and 1 drop of dil H2SO4 in 1ml of water is shaken with 10ml of ether] can be removed in several different ways. The simplest method is to pass dry ether through a column of activated alumina (80g AbOa/VOOml of ether). More commonly, IL of ether is shaken repeatedly with 5-lOml of a soln comprising... 

Oglialoro modification of, 708 Perkin triangle, 108, 218f Kon modification of, 109 Peroxides, detection of, in ether, 163 removal from diethyl ether, 163 removal from isopropyl alcohol, 886 Petroleum ether, purification of, 174 Phenacetin, 996, 997 1 10-Phenanthroline, 991, 992 p-Phenetidine, 997, 998 Phenetole, 665,670 Phenobarbitone, 1003,1004,1005 Phenol, 595, 613 Phenol aldehyde polymers, 1016 formation of, 1022 Phenolphthalein, 984, 985 action as indicator, 984 ... 

Organic peroxides are liable to detonate. Exposure of ethers, alkenes, and alkynes to air and light leads to peroxide formation. Distillation of these solvents poses an increased danger due to the concentration of peroxides in the still pot as the distillation proceeds. When present in small amounts, the peroxide is removed before distillation by the use of reducing agents such as ferrous sulfate in acidic aqueous solution. Peroxides may be detected by the addition of a few drops of aqueous 10% KI solution to a few mL of the ether. The presence of a peroxide is revealed by the appearance of the brown triiodide color. 

Some of the following material is taken from the second edition of this handbook from an article by Norman V. Steere, Control of Peroxides in Ethers. It has been edited to conform with the format of the current edition and has been added to from other sources. The sections on detection and estimation of peroxides and removal of peroxides have been substantially shortened, in line with the philosophy espoused elsewhere in this section to keep on hand only amormts that will be quickly used, and in order to reduce the risks in handling possibly contaminated materials. 

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). 

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. 

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

Ethers contain additives to stabilise them against peroxide formation. For instance, tetrahydrofuran is commonly stabilised by the addition of small amounts of hydroquinone. This absorbs uv radiation strongly and so interferes with uv absorbance detection. It can be removed by distilling the solvent from KOH pellets. If you use inhibitor-free tetrahydrofuran, it should be stored in a dark bottle and flushed with nitrogen after each use. Any peroxides that form should be periodically removed by adsorption onto alumina. 

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