(Hive Addict)
08-04-04 19:11
No 523636
(Rated as: good read)
J.Prakt.Chem. 5.1872;367-368 (http://visualiseur.bnf.fr/Visualiseur?D
If potassium pyrosulfate is heated to boiling with an alcoholic solution of sodium ethoxide for a longer time, quite much of a salt of ethylsulfuric acid is formed (Na or K). Because this salt is insoluble in absolute alcohol one proceeds as follows to identify it. After the long time of cooking, to the boiling liquid water is consecutively added so that the alcohol content sinks to 70-75%, boiling is kept up for some time, and finally the reaction mixture is filtered and evaporated. The remaining salt consists of the Na/K salts of carbonic, ethylsulfuric and traces of sulfuric acid. 96% ethanol ("Weingeist") dissolves mainly the ethylsulfuric acid salt.
Persulfates are OTC, cheap and the perfect precursors to pyrosulfates Post 519262 (psyloxy: "my last word on persulfate decomposition", Chemistry Discourse).
NaOEt is easy to make from OTC stuff Post 512239 (psyloxy: "some great alkali alkoxide patents", Chemistry Discourse).
--psyloxy--
(Moderator)
08-05-04 02:23
No 523705
(Rated as: good read)
From Cohen's Practical Organic Chemistry
Potassium Ethyl Sulphate, Dabit Ann. Chim. Phys. 1800, (r) 34, 300; Claesson, J. prakt. Chem. 1879 (2) 19, 246.
70 grms. (87 c.c.) absolute alcohol
50 grms. (27 c.c.) conc. sulphuric acid.
The alcohol is poured into a round flask (1/2 litre) and the sulphuric acid is slowly added and well mixed by shaking.
A considerable amount of heat is developed in the process. The flask is no fitted with a reflux condenser, placed upon the water bath and heated for 2-3 hours. The product now contains in addition to ethyl hydrogen sulfate, free sulphuric acid and unchanged alcohol. The liquid on cooling is poured into 1/2 litre of cold water in a large basin and well stirred. It is neutralized by adding chalk ground into a thin paste with water. This precipitates the free sulphuric acid as calcium sulphate and converts the ethyl hydrogen sulphate into the soluble calcium salt. The mixture is heated and filtered through a large porcelain funnel at the filter-pump, and the precipitate pressed well down. The clear filtrate is heated on a water-bath and a solution of potassium carbonate (about 50 grams) is added in small quantities until the liquid is slightly alkaline. To ensure complete precipitation a little of the clear liquid should be tested with a solution of potassium carbonate before proceeding.
The calcium salt is there1y converted into the soluble potassium salt and calcium carbonate is precipjtated. The latter is removed by filtration, as before, and the filtrate concentrated on water-bath to a small volume until a drop of the liquid, removed on the end of a glass rod, crystallizes at once on cooling. The potassium ethyl sulphate is filtered and washed with a little spirit or methylated spirit.
Crystallisation.- The substance should now be recrystallised. The success of many operations in practical organic chemistry depends upon skill in crystallisation. The first essential is to select a suitable solvent, that is, one which dissolves much more of the substance at a high than at a low temperature. To discover a suitable solvent a small quantity of the substance (0.1 gram is sufficient) is placed in a test-tube and a few drops of the solvent poured in. The common solvents are water, methyl and ethyl alcohol, ethyl acetate, acetic acid, acetone, benzene (also toluene and xylene) nitrobenzene, petroleum spirit and ligroin, chloroform and carbon tetrachloride. If the substance dissolves on shaking without warming or does not visibly diminish on boiling, it may be discarded as unsuitable. If it dissolves on heating or boiling and crystallises on cooling in considerable quantity, it may be employed. Sometimes solutions can be supercooled. In such cases, rubbing the sides of the test-tube with a glass rod will cause the substance to deposit. A convenient method of crystallisation may be occasionally employed by using two miscible solvents in one of which the substance is soluble and in the other insoluble. The substance is then dissolved in a small quantity of the first solvent and the second added gradually until a turbidity appears. Alcohol and water; and benzene and petroleum spirit are often used in conjunction in this way. If a substance of low melting-point is to be crystallised care should be taken that sufficient solvent is present to prevent the substance separating at a temperature at which it is still liquid. The interval of temperature may be increased after the solution has reached the ordinary temperature, by cooling it in a freezing mixture, when some of the solid will be deposited.
In the present instance spirit or methylated spirit (purified) will be found an efficient solvent for potassium ethyl sulphate. The following is the mode of procedure when a volatile or inflammable solvent is used: the substance is placed in a round flask attached to an upright condenser and heated on the waterbath. Small quantities of spirit are added and kept boiling until a solution is obtained. A small quantity of impurity may remain undissolved. The hot solution is at once decanted or filtered through a fluted filter or hot water funnel into a beaker and allowed to cool.
A fluted filter is made by first folding a large circular filter paper in the ordinary way. It is then half opened out and the the quadrants folded towards the middle line, This makes three creases with the hollows on the same side. The filter is now turned over and each section folded down the middle.
For the preparation of methyl potassium sulphate the same quantity of methyl alcohol is used; in other respects the two processes are identical. The yield is 45-50 grams.
Chemistry is our Covalent Bond