Hydrogen cyanide, caution

White precipitate of mercury (II) thiocyanate Blood red coloration due to complex formation Upon warming, red coloration is observed, with nitrogen oxide and hydrogen cyanide (caution toxic) being evolved Blue coloration due to complex ion formation... 

Cyanohydrins are highly toxic by inhalation or ingestion, and moderately toxic through skin absorption (21). AH a-hydroxy nitriles are potential sources of hydrogen cyanide or cyanides and must be handled with considerable caution. Contact with the skin and inhalation should be rigorously avoided. Special protective clothing should be worn and any exposure should be avoided (18,20). The area should be adequately ventilated. Immediate medical attention is essential in case of cyanohydrin poisoning. 

Caution Potassium cyanide is a potent poison, which should always be handled with gloves in a well-ventilated hood. Contact with acid releases toxic hydrogen cyanide gas. 

Caution This preparation must be conducted in a hood to avoid exposure to the poisonous hydrogen cyanide that is evolved. 

Caution The preparation should be carried out in a hood because hydrogen cyanide may be evolved. 

Facilities in each state that manufactured or processed hydrogen cyanide in 1992, the range of the maximum amounts stored on site, and the types of production or use activities (e.g., production for sale or on-site use in processing) are shown in Table 4-1 (TRI93 1995). The information in Table 4-1 is derived from the Toxics Release Inventory (TRI). The TRI data should be used with caution since only certain types of facilities are required to report. This is not an exhaustive list. No information is available in the TRI database for other cyanide and thiocyanate compounds in this profde because these compounds are not included under SARA, Title III and, therefore, are not among the chemicals that facilities are required to report (EPA 1993g). 

Caution Both tetracyanoethylene and tetracyanoethylene oxide slowly evolve hydrogen cyanide when exposed to water. Therefore all operations should be conducted in an efficient hood and contact with the skin should he avoided. 

Caution Carbonyl cyanide and water react with explosive violence to form hydrogen cyanide and carbon dioxide. This preparation should be carried out in a good hood with shielding, and rubber gloves should be worn. 

Caution. This synthesis should be carried out in a well-ventilated hood because of the use of highly poisonous hydrogen sulfide. Usual safety measures recommended for handling cyanide salts should be carefully observed during the synthesis and the disposal of the residues. Exposure of any of those products to acids could result in liberation of highly poisonous hydrogen cyanide. 

Caution. The reagents trimethyltriazacyclonane and trifluoromethane sulfonic acid are harmful by inhalation and by contact with skin. Potassium cyanide is highly toxic and produces volatile, poisonous hydrogen cyanide on protonation. All operations must be conducted in a well-ventilated fume hood. Wear appropriate protective clothing, gloves, and eye protection. 

Caution Because of the toxicity of hydrogen cyanide, this procedure should be conducted in a well-ventilated hood and rubber gloves should be worn. (See also Note 3.)... 

Caution Tetracyanoethylene slowly evolves hydrogen cyanide when exposed to moist air at room temperature. This material should he handled under a hood, and contact with the skin should be avoided. The first step in the preparation should also he carried out under a hood, since bromine is used. 

CAUTION Extreme care must be exercised when working with cyanide compounds. It is recommended that the worker wear gloves and perform all operations in a hood to minimize the escape of deadly hydrogen cyanide fumes into the laboratory. Cyanide residues should be rinsed down the drain with plenty of water Immediately after use.]... 

CAUTION Foaming This operation, as well as the rest of the experiment, MUST be carried out in a well-ventilated hood because vapors of hydrogen cyanide (from the excess of the potassium salt used) are liberated by the add.]... 

A few oilier inorganic chemicals, more frequently identified as multipurpose pesticides than as insecticides, do have very strong insecticidal properties. These compounds are used sparingly, often requiring special permits in some places, and with the greatest of safety cautions observ ed. Such compounds would include calcium cyanide, carbon bisulfide, carbon tetrachloride, hydrogen cyanide, paraformaldehyde, and phosphine. 

Dissolve 20 g (0.13 mol) of the cyano ester in 100 ml of rectified spirit and add a solution of 19.2g (0.295 mol) of pure potassium cyanide (CAUTION) in 40 ml of water. Allow to stand for 48 hours, then distil off the alcohol on a water bath. Add a large excess of concentrated hydrochloric acid and heat under reflux for 3 hours. (CAUTION hydrogen cyanide evolved.) Dilute with water, saturate the solution with ammonium sulphate and extract with four 75 ml portions of ether. Dry the combined ethereal extracts with anhydrous sodium sulphate, and distil off the ether. Recrystallise the residual acid from excess concentrated hydrochloric acid, and dry in the air. The yield of pure 2,2-dimethylsuccinic acid, m.p. 141-142 °C, is 12 g (63%). The p.m.r. spectrum is recorded in trifluoracetic acid and reveals signals at S 1.48 (s, 6H, Me2) and 2.92 (s, 2H, CH2) the hydroxyl proton is not observed. 

Method A (use of zinc cyanide). CAUTION The entire preparation should be conducted in an efficient fume cupboard. Tetrachloroethane is a potent poison and hydrogen cyanide is liberated during the reaction. 

Nitrogen and/or sulphur present. To remove cyanide and sulphide ions, make 2-3 ml of the fusion solution just acidic with dilute nitric acid, and evaporate to half of the original volume in order to expel hydrogen cyanide and/or hydrogen sulphide which may be present (CAUTION). Dilute with an equal volume of water and proceed as in test (1), (2) and (3) above. 

Thirty-five grams of mercuric acetate and 25 g. of ammonium thiocyanate are dissolved in 100 ml. of hot glacial acetic acid. A steady stream of hydrogen sulfide is conducted into the hot solution until precipitation is complete. Then the acetic acid is slowly evaporated. (Caution Hydrogen cyanide gas is evolved.) The black precipitate that first appears slowly changes to the red modification as the acid boils away. Until this change is... 

Cold dilute HCI Cyanides, CN Liberation of hydrogen cyanide odor of bitter almond (caution highly toxic)... 

Caution Hydrogen cyanide is extremely toxic and volatile. All manipulations of hydrogen cyanide and reactions thereof should be performed in a well-ventilated hood and care must be taken to avoid inhalation. 

Caution. This synthesis should be performed in the hood. Potassium cyanide hydrolyzes under appropriate conditions to generate hydrogen cyanide. 

Cyanomethylbenzoic acid. This preparation must be conducted in an efficient fitme cupboard. Into a 1-litre three-necked flask, provided with a mechanical stirrer and a thermometer, place 40 g (0.33 mol) of phthalide and 40 g (0.615 mol) of powdered potassium cyanide (CAUTION). Heat the stirred mixture to 180-190 °C (internal temperature) in an oil bath for 4-5 hours. Allow to cool, add 400 ml of distilled water and stir the mixture until all the solids are dissolved (about 1 hour). Filter off any unreacted phthalide. Add dilute hydrochloric acid (1 1) to the dark aqueous solution (CAUTION hydrogen cyanide is evolved) until it becomes turbid (about 20 ml are required), and continue the addition until the solution is slightly acid filter off any dark impurities which may separate. Neutralise the solution carefully with sodium hydrogen carbonate, add a few grams of decolourising carbon, stir the mixture for several minutes and filter. Acidify the nearly colourless filtrate with about 20 ml of concentrated hydrochloric acid, cool in ice and filter at the pump. The resulting o-cyanomethylbenzoic acid (36 g) melts at... 

B. 2-Bromo-3-methylbenzoic acid. Caution This procedure must be carried out in a hood with a good draft, because poisonous hydrogen cyanide gas is evolved. In a 5-1. round-bottomed flask are placed 90 g. of potassium cyanide, 900 ml. of 2-ethoxyethanol (Note 3), 850 ml. of water, and the moist 2-bromo-4-nitrotoluene obtained above. A reflux condenser is attached, and the mixture is boiled for 16 hours (Note 4). To the hot, dark-red solution is then added 1.51. of water, and the mixture is acidified with concentrated hydrochloric acid. (Caution Hydrogen cyanide is evolved.) The acidified mixture is boiled for 15 minutes to expel hydrogen cyanide and then allowed to cool to 35-40°. Five grams of diatomaceous earth is stirred in, and the mixture is filtered through a Buchner funnel precoated with a little diatomaceous earth. The solid is discarded, and the filtrate is extracted three times with 200-ml. portions of chloroform. The chloroform extracts are combined and extracted with three 100-ml. portions of 5% ammonium carbonate solution. The basic extracts are combined, acidified with concentrated hydrochloric acid, and cooled in an ice bath. The oil which first forms soon crystallizes. 

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