Hydrocyanic acid, determination

Methanol can be converted to a dye after oxidation to formaldehyde and subsequent reaction with chromatropic acid [148-25-4]. The dye formed can be deterruined photometrically. However, gc methods are more convenient. Ammonium formate [540-69-2] is converted thermally to formic acid and ammonia. The latter is trapped by formaldehyde, which makes it possible to titrate the residual acid by conventional methods. The water content can be determined by standard Kad Eischer titration. In order to determine iron, it has to be reduced to the iron(II) form and converted to its bipyridyl complex. This compound is red and can be determined photometrically. Contamination with iron and impurities with polymeric hydrocyanic acid are mainly responsible for the color number of the merchandized formamide (<20 APHA). Hydrocyanic acid is detected by converting it to a blue dye that is analyzed and deterruined photometrically. 

The determinations ol importance In the oxaminaliou of this oil are ((1) tbedetermiuadouof chlorine, or at all events its detection qualitatively, it present (2) the determination of benzaldchyde, and (3) the determioa-tlou ol hydrocyanic acid. 

For an exhaustive examination of the various processes proposed for the determination of hydrocyanic acid, the reader is referred to a series of papers by Eunne in the Apotheker Zeitung.-... 

By simply hydrolyzing the easily accessible 2-hydroxy-2-methylalkanenitriles with concentrated acid, 2-hydroxy-2-methylalkanoic acids are obtained without measurable racemization (Table 3). The reaction sequence from the starting ketone to the carboxylic acid can be carried out in one pot without isolation of the cyanohydrin. The enantiomeric excesses of the (/ )-cyanohydrins and the (ft)-2-hydroxyalkanoic acids are determined from the ( + )-(/T)-Mosher ester derivatives and as methyl alkanoates by capillary GC, respectively. The most efficient catalysis by (R)-oxynitrilase is observed for the reaction of hydrocyanic acid with 2-alkanoncs. 3-Alkanoncs are also substrates for (ft)-oxynitrilase, to give the corresponding (/ )-cyanohydrins32. 

The liberation of hydrocyanic acid due to complete hydrolysis of cyano-genic glycosides can be determined by a simple colour test using sodium picrate paper (yellow), which turns red (sodium isopurpurate) in contact with HCN. 

Detection and Determination,—-The detection of hydrocyanic acid is oftentimes of die greatest importance, especially in cases of poisoning. Of late years, chemistry has, in this respect, given evidence moet important and incontrovertible. 

J.6 Determine the salt that is produced from the acid-base neutralization reaction between (a) potassium hydroxide and acetic acid, CH3COOH (b) ammonia and hydroiodic acid (c) barium hydroxide and sulfuric acid (both H atoms react) (d) sodium hydroxide and hydrocyanic acid, HCN. Write the full ionic equation for each reaction. 

This consists essentially of sugar and almond paste. Besides the determination of the sugars, which is made as in biscuits, and the microscopic examination for the detection of other seeds and extraneous flours, tests for hydrocyanic acid (from the bitter almonds) and nitrobenzene (added as an adulterant) are also necessary. 

The tests to be made on spirits and liqueurs include a certain number which are common to all these products, such as determinations of the alcoholic strength, extract and ash, and tests for impurities and denaturing agents other investigations are made only with certain products, examples of these being the examination of kirschwasser for hydrocyanic acid, the determination of sugars in liqueurs, etc. The former are treated under General Methods and the latter in the Special Part. 

The methods of analysis are those used for other spirits in addition, for nut-fruit spirits, hydrocyanic acid and benzaldehyde and sometimes nitrobenzene are tested for and determined as follows ... 

B) Quantitative Determination. In spirits from nut-fruits, the hydrocyanic acid is partly free and partly combined with benzaldehyde (cyanohydrin). That in the latter form is determined indirectly as the difference between the total and free amounts. 

The total hydrocyanic acid is determined similarly, but after the cyanohydrin of benzaldehyde has been decomposed. For this purpose, 100 c.c. of the spirit in a 300 c.c. flask are rendered strongly alkaline with ammonia and then treated with a measured excess of the silver nitrate solution. The whole is shaken, immediately acidified with dilute nitric acid and diluted to the mark, an aliquot part of the filtered liquid being then treated as in the determination of the free hydrocyanic acid. 

The above methods cannot be used if the spirit contains chlorides, as may happen if it has been broken down with water containing these salts. In this case the total hydrocyanic acid may be determined by distilling 100 c.c. of the spirit and collecting at least three-quarters (which will contain all the hydrocyanic acid present) in a dilute solution of silver nitrate of known titre. The liquid is then made up to a definite volume and filtered, the excess of silver in an aliquot part of the filtrate being titrated with thiocyanate as already described. The free hydrocyanic acid, in presence of chlorides, should be determined colorimetrically as follows a solution of about 0-05 gram of potassium cyanide per litre is prepared and its exact content of HCN determined by titration with silver nitrate and ammonium thiocyanate. In a series of test-tubes are placed such quantities of this... 

With his colleague Louis-Jacques Thenard (1777-1857), Gay-Lussac did considerable work with electrochemistry to produce significant amounts of elemental sodium and potassium, highly reactive and useful substances that were used to isolate and discover the element boron. Gay-Lussac also completed extensive studies of acids and bases and was the first to deduce that there were binary (two element) acids such as hydrochloric acid (HC1) in addition to the known oxygen-containing acids like sulfuric acid (H2S04). Additionally, he was able to determine the chemical composition of prussic acid to be hydrocyanic acid (HCN) and was considered the foremost practitioner of organic analysis. 

Lithium cyanide has not been isolated, but Varet6 has determined its heat of formation from the hydroxide and hydrocyanic acid ... 

Voto6ek and Wichterle " investigated the reaction of JV-substituted gly-cosylamines with hydrocyanic acid, but they did not start with the isolated glycosylamine. The sugar and amine were heated in alcohol, the hydrocyanic acid was added, and the mixture was allowed to cool. The structure of the crystalline nitrile isolated was not determined. Because the hydrogen cyanide could have added to the carbonyl group of the ketose after an Amadori rearrangement had occurred, the constitution of their products is open to question. 

Hydrocyanic acid may be determined gravimetrically, volumetrically or colorimetrically. 

Gravimetric Methods. These methods are seldom employed because of their laborious nature. In any case, their use is advisable only when the quantity of hydrocyanic acid to be determined is not too small. Of these methods, the procedure of Rose is the most generally employed. ... 

In order to carry out this determination, not more than o-i gm. free hydrocyanic acid is treated with a few ml. of sodium hydroxide solution and 0 5 gm. sodium bicarbonate and made up to a volume of 50 ml. with water. The titration is carried out with decinormal silver nitrate solution, shaking until finally a slight permanent opalescence remains. 

The sample is treated with an exactly measured quantity of standard arsenious acid solution in excess and an excess of a 15% solution of sodium hydroxide. The liquid is warmed on the water-bath, and while still hot a slow current of carbon dioxide is passed through until the hydrocyanic acid is completely eliminated. The solution is then allowed to cool and made up to a convenient volume. The excess of arsenious acid is then determined in an aliquot of this by addition of sodium bicarbonate and titration with a standard solution of iodine. 

The Michael addition of anions of C-acids, such as acetylacetone or hydrocyanic acid, to phenyl vinyl ketone follows a scheme similar to (7). In the cases studied it was possible to neglect the acid-base properties of the adduct and the reverse elimination reaction (Hrubcova, 1964). Equations analogous to (9) and (10) were used and the pH-dependence of the determined formal rate constant at a given analytical concentration of the C-acid follows a dissociation curve with an inflexion at the pKa value of the C-acid. 

A complete quantitative mechanism cannot be constructed with confidence on the basis of the products since not all of them were determined. A variety of secondary processes is likely. Hydrogen abstraction is expected to involve mainly the N-bound H atom. The activation energy for abstraction by methyl is given as 4.8 kcal/mol (277). Reaction 85 has been found (277) to yield ethylene and nitrogen in the radical-sensitized decomposition of ethyleneimine. Reaction 70 (see above) could explain the production of hydrocyanic acid. 

Fcrrocyanide. Results from the ferrocyanide tests are shown in Table V. Iron is reduced in the approximate amounts determined by the design except in the last test where the residual iron is probably due to excess potassium ferrocyanide. The concentrations of both cadmium and nickel are reduced below the detectable limits of the analytical method even at the lowest stoichiometry tested. These results indicate that even lower amounts of ferrocyanide could produce substantial reduction in heavy metal concentrations. However, this method has two primary disadvantages (1) the potential reaction of ferrocyanides with strong acids to form hydrocyanic acid (HCN) and (2) the... 

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