Preparation of Alkyl Nitrites from Primary Alcohols v2.0

by Eleusis

This document describes the general process for preparing an alkyl nitrite from an alcohol with the same parent group:

R-OH =NaNO2/H2SO4=> R-ONO + NaSO4 + H2O

Three examples will be presented, though any primary alcohol may be substituted. The emphasis here is on the practical aspects of production, theory can be found elsewhere ;-).

All of the alkyl nitrites are unstable and should be used as soon as possible (within days). Longer storage is possible by dissolving them into their forming alcohol and keeping them in the freezer (a couple of weeks). They decompose into the alcohol, CO2 and water.

I have improvised the apparatus required to make the gaseous nitrites (basically just methyl) for this edition and have found that a couple of tupperware containers arranged like so works perfectly:

  /  \
 |    | <- Addition Funnel
 |    | _____________________
  \  / | ___________________ | <- Polypropylene tubing
   ||  ||                   ||
-----------                 ||
|  ||  || |                 ||   || <- Exhaust vent
|  ||     |              ------------
|  ||     |              |  ||      |
|  ||     |              |  ||      |
|  ||     |              |  ||      |
|  ||     |   Aquarium   | /  \     |
|  ||     |   Bubbler -> | \__/     |
 ---------                ----------

Use a stirrer magnet, preferably in both containers, but at least the first one, to make for a nearly worry free setup that requires little or no babysitting. Suggested improvements from my horrible ascii drawing would be to use multiple aquarium bubblers and a homemade pressure equalized plastic addition funnel (I rigged up a pressure return for a regular sep. funnel in my setup by running some tubing from the top of the first tupperware flask to a cork plugged into the top of the funnel). It has been my experience that if the reaction is not carried out too virgorously (in other words, you follow my directions) that there are no pressure sealing problems whatsoever.

Methyl Nitrite from Methanol

Prepare a solution of 1.25 moles Sodium Nitrite (90g 97%), .64 moles Methanol (21g), and enough water to make 350mL total volume (Solution I).

Prepare a second solution of .61 moles conc. Sulfuric Acid (62g), 3 moles Methanol (9.8g), and enough water to make 350mL total volume (Solution II).

Pour Solution I and a stirrer magnet into a 1L Erlenmeyer flask and plug with a two-hole rubber stopper. Insert a short piece of glass tubing into one hole for the gas take-off, and another longer piece which extends close to the bottom of the flask for adding Solution II. Use a piece of polypropylene tubing to connect the addition tube to a 500mL separatory funnel suspended above the flask. With the valve on the funnel closed, fill the funnel with Solution II.

Pour 500mL of Methanol into a beaker and suspend a glass funnel upside down about .5cm below the alcohol surface as a gas bubbler. Connect the funnel to the reaction flask with polypropylene tubing.

Turn on the magnetic stirrer then adjust the stopcock on the separatory funnel so that Solution II flows at a slow, steady rate into the flask below (1 or 2 drops per second seems fine). Swirl the bubbler until occasionally to insure the nitrite dissolves well until done.

Note: It has been my experience that after much of Solution II has been added to Solution I, the whole mixture will start foaming quite a bit. If this foam makes it into the bubbler, you might as well call it quits. I can suggest four options to combat this problem, your own ingenuity may do me better: 1) Fashion a "shield" to block the rise of the foam; 2) Use a trap between the reaction flask and the bubbler flask; 3) Use an extra large flask for the reactants; 4) Reread the beginning of this document to see the Tupperware setup which works fine and is cheap as well.

The Methyl Nitrite produced is *unstable* and should be protected from heat, sunlight, and other chemicals. Stopper the second flask and use within 2 weeks. The total amount of Methyl Nitrite produced will be approximately 1.25 moles dissolved in the 500mL of corresponding alcohol. In the reaction flask the solid byproduct is Sodium Sulfate, which can be dried in an oven at 200C and used as a mild dessicant elsewhere.

Ethyl Nitrite from Denatured Alcohol

A better approach for producing Ethyl Nitrite has been found and is significantly easier than either making Methyl or n-Butyl Nitrite. Ethyl Nitrite boils at 17C, so instead of bubbling the gas into the forming alcohol, we collect it as a liquid over ice, and then add it to the alcohol for storage.

Dissolve .55 mole (38g) of Sodium Nitrite in 120mL of water and chill in the freezer to 0C (Solution I).

Pre-chill a solution of 29mL water and 33mL (25g/~.5 moles) of denatured alcohol (90% ethanol, 5% methanol, 5% water) or 29mL of the azeotrope (~95% ethanol, 5% water). Carefully add 25g Sulfuric Acid to this solution and chill to 0C (Solution II).

Mix up a solution of 250mL 2% Sodium Bicarbonate and chill this and a 500mL separatory funnel in a freezer.

Set up a round bottom flask with a claisen adapter, "modified" addition funnel (fit a piece of heat-shrink tubing onto the center outlet stem of the funnel so that it can be threaded down the claisen adapter to the bottom of the rb flask). Situate the flask in an ice/salt bath and add Solution I with a stirrer magnet. Once the flask contents have cooled to -10C, add the chilled Solution II slowly while stirring over the course of approx. 30 minutes. After this, transfer the reaction mixture to the chilled separatory funnel and run off the aqueous phase. Wash the nitrite layer with the chilled 2% Sodium Bicarbonate solution in three parts. If desired, dry over anhydrous Sodium Sulfate and store in the freezer or dissolve in an equal weight of ethanol to make a 50% solution. Yield is approx. .5 mole. It decomposes at it's bp.

n-Butyl Nitrite from n-Butanol

Place a 1L round bottom flask (either 3-neck or in conjunction with a claisen adapter) into an ice/Calcium Chloride bath. Add 450mL of water and 1.64 moles Sodium Nitrite (117g 97%) to the flask. Drop in a stirrer magnet, insert a thermometer into either the center tube of the claisen adapter of one of the necks if using a three-neck flask and stir until the temperature of the solution drops to 0C or below. Prepare a second solution of 30mL water, .75 moles conc. Sulfuric Acid (77g) and 1.5 moles of n-Butanol (110g/137mL) which has been chilled to 0C also (Add in that order!). Ideally, with the three necked flask, this solution is added below the surface, but with sufficiently vigorous stirring and a slow enough rate, it can be done satisfactorily with the claisen setup. Either way, a separatory funnel is loaded with the second solution, and it is added to the flask at a slow enough rate so that no gas evolves and such that the reaction temperature does not vary more than +/- 1C. With the three-neck flask setup, this should take between 1.5 to 2 hours. The claisen setup may take up to four. After all of second solution has been added, turn off the stirrer and let the solution separate into 2 layers while still on the ice bath. Decant the two layers from the Sodium Sulfate solids into a separatory funnel. The aqueous layer will be on bottom and should be removed. The remaining n-Butyl Nitrite layer should then be washed in the funnel with 2 25mL portions of a 50mL solution of 1g Sodium Bicarbonate and 12.5g Sodium Chloride in water. The n-Butyl Nitrite may then be dried over 10g anhydrous Sodium Sulfate, or used as is in reactions involving water. The yield should be 80-85% of the expected, or 1.25-1.5 moles actual.

- - The Alkyl Nitrite Doc - 09/01/95 -

Addendum by Sunlight 980608:

Also if you try to make MeONO as Eleusis say, you will make MeONO, but if you don't use a magnetic stirrer in flask II, it will escape, it won't dissolve. Generation of MeONO is more flexible than this, methanol is not needed in the sulphuric solution. There is a typographical error also: "Prepare a second solution of .61 moles conc. Sulfuric Acid (62g), 3 moles Methanol (9.8g), and enough water to make 350mL total volume (Solution II)" Three mols of methanol are not 9.8 grams, but 98 grams (96 with my calculator) In the same text, Eleusis said there are 1.25 mols of MeONO dissolved in 0.5 liters of methanol. My experience is that is impossible to dissolve more than 8-10 grams in 100 cc of methanol at 20C, weighting it. At this point, weight is constant, increases and decreases around. 1.25 mols are 76,25 grams, too much for me. I think Eleusis didn't weight his solution.