Sciencemadness Discussion Board

Efficiency and Mad Science

Polverone - 3-3-2004 at 12:38

From Muspratt's Chemistry as Applied to the Arts and Manufactures, 1860:
Quote:
In the conversion of sugar or sirup into oxalic acid, one may use either vessels of earthenware or wooden tanks lined with lead. The former are generally made to hold about two gallons each, and are set in large numbers in a stout water-bath built of brickwork, which is lined with lead or cement, and heated by coils of steam-piping. The wooden tanks are generally about eight feet square by three feet deep, each being heated by about forty-eight feet of one-inch steam pipe. They should be provided with large taps placed at the bottom to draw off the liquor into the crystallizing pans.

The vessels are now charged with the sugar or sirup, and nitric acid is added. The usual proportions are -- to every hundredweight of sugar as much nitric acid as can be obtained from five hundredweight of nitrate of potassa, and two and a half or about three hundredweight of sulphuric acid. The nitric acid should have a specific gravity of from 1.200 to 1.270. If a more concentrated acid is employed great loss is occasioned, since a large part of the sugar is then converted, not into oxalic, but into carbonic acid. The tanks are then heated to about 125 degrees (Fahrenheit). If the operation is properly managed, there will be a moderate, steady disengagement of gas, and a very faint smell of nitric oxide, but no appearance of orange fumes. A slight addition of sulphuric acid is generally considered advantageous. When the operation is at an end, the liquid is let off into shallow cooling tanks, which are also made of wood, and lined with lead, and is there allowed to crystallize. The mother liquor is run off from the crystals, and added to the materials in the next operation. The crystals are carefully drained, washed, dried in a stove, and if necessary, redissolved and recrystallized. The yield is variously stated; one hundredweight of good brown sugar affording, according to some, fifty to sixty pounds; according to others, one hundred and forty pounds of acid. If, however, the process is properly conducted, and the crystals freed from moisture and nitric acid, the result will be about one hundred and twenty-five pounds.


From Arthur J. Hale's The Synthetic Use of Metals in Organic Chemistry, 1914:
Quote:
OXALIC ACID.
[J. Prakfc. Chem., 1907, 75, 146.]
Concentrated nitric acid (140 c.c.) containing vanadium pentoxide (0.1 grm.) is warmed gently in a litre-flask; it is then placed in a fume-cupboard and powdered cane-sugar (20 gms.) is added. As soon as the reaction becomes vigorous and brown fumes are evolved, the flask is placed in cold water to moderate the reaction. The mixture is allowed to stand for twenty-four hours, by which time the oxalic acid will have crystallised; the crystals are drained and recrystallised from water. Yield, about 16 gms.


From Mann and Saunders Practical Organic Chemistry, 1960:
Quote:

Oxalic Acid
Required: Cane sugar, 20 g.; nitric acid, 100 ml. Owing to the copious evolution of nitrous fumes, this preparation must be carried out in a fume-cupboard having an efficient draught. Place 20 g. of coarsely powdered cane sugar (sucrose) in a 750 ml. flat-bottomed flask, add 100 ml. of concentrated nitric acid and heat the flask on a boiling water-bath. As the mixture becomes warm, the greater part of the sugar dissolves and a vigorous but harmless reaction, accompanied by a tremendous evolution of nitrous fumes, takes place. Immediately the evolution of gas starts, remove the flask from the water-bath and place it on a wooden block or some similar non-conducting surface. When the reaction subsides (after about 15 minutes) pour the hot solution into an evaporating-basin, wash out the flask with about 20 ml. of concentrated nitric acid, and then evaporate the acid solution on the water-bath until it has a volume of about 20 ml. Some oxidation continues in the solution during the evaporation, which is comparatively rapid. Now add about 40 ml. of water to the solution, and again evaporate to about 20 ml. Cool the solution thoroughly in ice-water; oxalic acid rapidly crystallises. When crystallisation is complete, filter at the pump, and then recrystallise from a small quantity of hot water. Dry by pressing between pads of drying-paper, or in an atmospheric desiccator, but not in an oven where partial loss of water of crystallisation may occur. Yield, 7 g.


Some authors call azeotropic (68%) nitric acid "concentrated"; others reserve this for more concentrated mixtures. I will assume that the above preparations calling for "concentrated" acid refer to 68%, since more concentrated acid is much less common. With a specific gravity of 1.42 and 68% HNO3 by weight, we see that the procedure reported by Mann and Saunders uses 97 grams of HNO3 to produce 7 grams of oxalic acid, and that of Hale uses 135 grams of HNO3 to produce 16 grams of oxalic acid.

Muspratt is a bit harder to decipher, given his dated terminology. However, if we assume 95% recovery of HNO3 from KNO3, it appears that his procedure uses 296 pounds of HNO3 (and about as much H2SO4) to produce 125 pounds of oxalic acid.

Muspratt's 1860 method produces 0.42 g of oxalic acid with a gram of HNO3.
Hale's 1907 method produces 0.12 g of oxalic acid with a gram of HNO3.
Mann's 1960 method produces 0.07 g of oxalic acid with a gram of HNO3.

Mann's preparation is extremely inefficient but well-suited in its simplicity and speed to serving as an example preparation for students. Hale's preparation is considerably more efficient, but uses a catalyst and allows 24 hours for crystallization. Muspratt's preparation is by far the most efficient, but also by far the most involved and time-consuming, for it is describing an industrial process of the mid-19th century.

Mad Scientists tend to fall somewhere between chemistry students and industrialists in needs. For most of us, time is an abundant resource, so methods that require patience but are more efficient in their use of reagents (and hence money) are often preferred. We aren't commercially motivated, but we may have to become our own suppliers in making chemicals that aren't readily available for reasons of expense or regulation. Reactions that scale up poorly - such as the oxalic acid preparations of Hale and Mann - are therefore also less desireable. Who would want to make a kilogram of oxalic acid using the method of Mann, 7 grams at a time, even if HNO3 were free?

Textbooks of practical organic chemistry, preparations from Organic Syntheses, and methods drawn from rhodium.ws (which itself uses the two previous sources) may all work as described, and in fact may be adequate depending upon your needs. But don't hesitate to keep looking deeper and further back to find better methods. Newer is not always better, and "lab scale" is not always better than "industrial" (if "industrial" can be scaled down without too much difficulty). Only Mad Scientists truly understand the demands of Mad Science.

Marvin - 3-3-2004 at 19:24

A good point, but it also brings up the question of if anyone would want to use up sugar and nitric acid at all when they can use sawdust and sodium hydroxide draincleaner. Albei it with a more laborious purification procidure. Or for that matter buy it as ferric chloride stain remover from home electronics suppliers.

It would be nice if more information online was posted with yeilds, enabling us to make comparasons as above for processes that arnt as widely known.

oxalic acid

Magpie - 3-3-2004 at 20:24

When in Sears the other day I saw bottles of a cleaner in the water softener/humidifier section that listed the only ingredient as oxalic acid. IIRC it was about $1/oz.

I see your point about the unique needs of Mad Scientists. I think the terms clandustrial priest and vulture chemist are particularly appropo in this regard. (Credits to Organikum and vulture, repectively.) I have become an avid label reader now when in any store, even Wal-Mart. I get a certain thrill in knowing that I will be using the product for a use that it was not intended - a higher use.

BromicAcid - 4-3-2004 at 16:48

I bought a can of oxalic acid 2 lbs for $3.99 from a pharmacy, it was for cleaning straw hats. Ingredients listed at 100% Oxalic Acid, yeah right, no one ever gets 100%! Maybe 99.995% but the cost for that superfine chemical would be crazy.

Regardless, being an at home chemist steps into the economic relm more then we like. Weighing how much it costs to make to what value we get from it and what we can make from it and how much we can buy it for. But sometimes its worth the price to avoid the hassel.

errata

Magpie - 4-3-2004 at 18:24

My previous post about oxalic acid at Sears was in error. What is actually there is sulfamic acid for $7/12 oz and citric acid for $20/38 oz.