Post by Anders Hoveland on Feb 1, 2011 13:02:21 GMT -8
Solid hydroxylamine is both unstable and very hygroscopic, and relatively volatile (melts at 33 C and boils at 58 C). The hydrochloride salt is more stable and storable.
If separate solutions in ethanol of hydroxylamine hydrochloride and potassium hydroxide are prepared, then mixed, potassium chloride will be precipitated, which can be filter off. Thus a fresh solution on NH2OH in ethanol can be obtained, which can immediately be used and is much more stable.
While hydroxylamine (H2NOH) is easily accessable to organic chemists working at institutions, and is not to difficult to obtain for the home experimenter, I feel there is a void of online information existing about the chemistry of synthesis for this widely used and mentioned regent. I am reluctant to start a new post, but could not find a a good existing good topic to put this.
Preparation of Hydroxylamine using the Meyer disproportionation reaction
Nitromethane reacts, when heated with 30% concentrated sulfuric acid solution, to form formic acid and hydroxylamine sulfate.
Preparation of Hydroxylamine hydrochloride by reduction of nitrite, using sulfur dioxide
40g potassium nitrite (KNO2) and 50g potassium acetate (CH3COOK) are dissolved in 100ml ice water. 750g finely crushed ice is added. Into this solution a stream of sulfur dioxide (SO2) is bubbled until the solution smells of SO2. The temperature must be kept below 0°C through the whole reaction. The salt of K2[HON(SO3)2] separates and is filtered off and washed with ice water. The salt is dissolved in 500ml 0.5 M HCl and boiled for two hours. Still boiling a solution of Barium chloride (BaCl2) is added as long as barium sulfate (BaSO4) precipitates ( CaCl2 may possibly work instead). The BaSO4 is filtered off and the clear filtrate is evaporated to dryness. The residue consists of Potassium Chloride (KCl) and NH2OH*HCl. Anhydrous ethanol(EtOH) is used for extraction of the Hydroxylammonium chloride, the KCl remains undissolved. The EtOH is evaporated on a water bath and the product can be recrystallised from water (mp 151°C).
Mix cold saturated solutions containing one molecular proportion of sodium nitrate, and two molecular proportions of acid sodium sulphite, and then adding a saturated solution of potassium chloride to the mixture. After standing for a day, hydroxylamine potassium disulphonate crystallizes out. This is boiled for some hours with water and the solution cooled, when potassium sulphate separates first, and then hydroxylamine sulphate.
Preparation of Hydroxylamine using the oxime process
Sodium hypoclorite (bleach) and ammonium hydroxide react to produce chloramine gas (NH2Cl). This unstable poisonous is then bubbled into a solution of methylethylketone and sodium ethoxide dissolved in pure alcohol. (The sodium ethoxide can be prepared by adding solid NaOH pure alcohol. After several hours, the bottom will consist of solid hydrated NaOH, a small layer of water saturated with NaOH will form immediately above, and the top layer will consist of pure alcohol with the associated sodium ethoxide dissolved in it. The top lay is decanted out. Alternatively, Na2CO3, used to regulate pH for use in pools, and CaO, used as cement lime can be used instead of solid NaOH, 90% concentrated alcohol can then be used )
The chloramine gas reacts with the methylethylketone and sodium ethoxide to form O-ethyl-methylethyloxime, with a structure CH3CH2ON=C(CH3)CH2CH3.
The byproduct, NaCl, precipitates out at the bottom at this time, since it is not soluble in alcohol. The progress of the reaction can be estimated by the formation of the solid byproduct.
Cool the contents and allow an hour for all the NaCl to settle at the bottom, then decant out the liquid into a separate container, leaving the all solid at the bottom in the first container. The O-ethyl-methylethyloxime then hydrolyzes with a 20% solution of sulfuric acid to form hydroxylamine sulfate. This will mostly precipitate out at the bottom if only a small amount of the acid solution is added.
If separate solutions in ethanol of hydroxylamine hydrochloride and potassium hydroxide are prepared, then mixed, potassium chloride will be precipitated, which can be filter off. Thus a fresh solution on NH2OH in ethanol can be obtained, which can immediately be used and is much more stable.
While hydroxylamine (H2NOH) is easily accessable to organic chemists working at institutions, and is not to difficult to obtain for the home experimenter, I feel there is a void of online information existing about the chemistry of synthesis for this widely used and mentioned regent. I am reluctant to start a new post, but could not find a a good existing good topic to put this.
Preparation of Hydroxylamine using the Meyer disproportionation reaction
Nitromethane reacts, when heated with 30% concentrated sulfuric acid solution, to form formic acid and hydroxylamine sulfate.
Preparation of Hydroxylamine hydrochloride by reduction of nitrite, using sulfur dioxide
40g potassium nitrite (KNO2) and 50g potassium acetate (CH3COOK) are dissolved in 100ml ice water. 750g finely crushed ice is added. Into this solution a stream of sulfur dioxide (SO2) is bubbled until the solution smells of SO2. The temperature must be kept below 0°C through the whole reaction. The salt of K2[HON(SO3)2] separates and is filtered off and washed with ice water. The salt is dissolved in 500ml 0.5 M HCl and boiled for two hours. Still boiling a solution of Barium chloride (BaCl2) is added as long as barium sulfate (BaSO4) precipitates ( CaCl2 may possibly work instead). The BaSO4 is filtered off and the clear filtrate is evaporated to dryness. The residue consists of Potassium Chloride (KCl) and NH2OH*HCl. Anhydrous ethanol(EtOH) is used for extraction of the Hydroxylammonium chloride, the KCl remains undissolved. The EtOH is evaporated on a water bath and the product can be recrystallised from water (mp 151°C).
Mix cold saturated solutions containing one molecular proportion of sodium nitrate, and two molecular proportions of acid sodium sulphite, and then adding a saturated solution of potassium chloride to the mixture. After standing for a day, hydroxylamine potassium disulphonate crystallizes out. This is boiled for some hours with water and the solution cooled, when potassium sulphate separates first, and then hydroxylamine sulphate.
Preparation of Hydroxylamine using the oxime process
Sodium hypoclorite (bleach) and ammonium hydroxide react to produce chloramine gas (NH2Cl). This unstable poisonous is then bubbled into a solution of methylethylketone and sodium ethoxide dissolved in pure alcohol. (The sodium ethoxide can be prepared by adding solid NaOH pure alcohol. After several hours, the bottom will consist of solid hydrated NaOH, a small layer of water saturated with NaOH will form immediately above, and the top layer will consist of pure alcohol with the associated sodium ethoxide dissolved in it. The top lay is decanted out. Alternatively, Na2CO3, used to regulate pH for use in pools, and CaO, used as cement lime can be used instead of solid NaOH, 90% concentrated alcohol can then be used )
The chloramine gas reacts with the methylethylketone and sodium ethoxide to form O-ethyl-methylethyloxime, with a structure CH3CH2ON=C(CH3)CH2CH3.
The byproduct, NaCl, precipitates out at the bottom at this time, since it is not soluble in alcohol. The progress of the reaction can be estimated by the formation of the solid byproduct.
Cool the contents and allow an hour for all the NaCl to settle at the bottom, then decant out the liquid into a separate container, leaving the all solid at the bottom in the first container. The O-ethyl-methylethyloxime then hydrolyzes with a 20% solution of sulfuric acid to form hydroxylamine sulfate. This will mostly precipitate out at the bottom if only a small amount of the acid solution is added.