Sciencemadness Discussion Board - thermal decomposition of acetyl salicylic acid?

thermal decomposition of acetyl salicylic acid?

obsessed_chemist - 5-8-2009 at 18:32

Hello all. I recently came across the mentioning of a patent dealing with the synthesis of salicylic aldehyde. The method involves slowly heating acetyl salicylic acid to about 200-210 C, over the course of 5-6 hrs, and in an open vessel. Then, the whole thing is cooled, boiled with portions of water, the residue then dissolved with acetone, and precipitated by then adding to a large volume of water.

When I first read this, I thought that it must somehow be a misprint/bunk, etc. However, I have found two references to the particlar patent from google books, copied from ancient chemistry literature. It seems impossible since ortho-hydroxybenzaldehyde (salicylaldehyde) lists a b.p. of 195.5 C in modern chem lit., but I've seen it listed higher in older literature. Perhaps this temperature is meant towards the tail end of the reaction, and/or that the impurities present interfere with the b.p. somehow. I'm totally stumped.

Another detail I find puzzling is how in fact such a reaction proceeds; I'm thinking that perhaps somehow that for every two molecules of aspirin, the two acetyl groups combine with H2O taken from the two formic acid groups, which then combine to form one molecule of salicylic anhydride, as the two acetyl groups are hydrolized into hydroxy groups, acetic acid being the by-product.

However, even with that being the case with this alleged reaction's course of action, wouldn't salicylic anhydride (if formed) hydrolize with water to form the acid, not the aldehyde? BTW, the only reason I'm suspecting this reaction mechanism is because I've seen mention of reducing benzoic acid to benzoic anhydride via heating/distilling with acetic anhydride. So what's going on here?

Besides the scant details available from these sources, I have been unable to obtain the original patent to confirm anything. The other peculiar thing is that the sources I've found list two different patent dates, but under the same names. One lists: August 13, 1901; the other: August 07, 1902. The patent number by the way is: Eng Pat. 20,188.

Here is the main link (I lost the other one - google should turn it up with right key words):

http://books.google.com/books?id=5nnPAAAAMAAJ&pg=PA618&a...

Page 618, if the link doesn't take you directly.

[Edited on 8/6/2009 by obsessed_chemist]

[Edited on 8/6/2009 by obsessed_chemist]

obsessed_chemist - 5-8-2009 at 18:42

Also worth noting, I believe acetyl salicylic acid had been discover/isolated at or around 1888 or so, and that Bayer didn't patent it as a pain reliever until 1899, so it's not impossible to believe that 2-3 years later, a technique using it as a chemical feedstock for the aldehyde would be, at that time, feasible. I believe that before that time, the aldehyde was obtained by the oxidation of salicilin. All of these salicyl-related names sure do confuse matters a bit!

I'm almost ready to chalk this up as a misprint, unless someone can enlighten me otherwise.

Oh, and here's the other reference:

http://books.google.com/books?id=8EHOAAAAMAAJ&pg=PA1194&...

pg. 1194

[Edited on 8/6/2009 by obsessed_chemist]

Nicodem - 5-8-2009 at 23:19

To me, your links don't bring me anywhere. Please post the page excerpt and the references cited in these books (use the print screen function if you can't do it in any other way).

I can't understand much from what you wrote. It does not make much sense to me. Essentially, you say that the thermolysis of aspirin was claimed to produce salicaldehyde? But then you go on mentioning formic acid and so on... well, we really need to see what you are talking about.

I don't even know what country's patent is "Eng Pat. 20,188" supposed to be. A patent search at espacenet by using only the number 20188 gives 36 patents but none is related to this topic.

The thermolysis of aspirin was briefly mentioned in the thread about acetanhydride. The products are polyesters along with other stuff.

obsessed_chemist - 6-8-2009 at 07:02

Sorry for the confusion. I don't know why the links aren't working, but I have simply decided to copy + paste to text from the html form, because cropping and editing the print screens for both references without exceeding the 2MB limit proved to be difficult with the use of microsoft paint.

This first reference is is made on p. 618 of Thomas Edward Thorope's A Dictionary of Applied Chemistry I also included here some unrelated methods to salicylaldehyde, from the same page, simply to show some contrast:

Quote:

SALICYLALDEHYDE (' salicylide ')

C,H4(OH)CHO (1, 2).

Occurs in the oil from Spir&a Vlmaria (Linn.) and other species of Spircca. Obtained, along with the isomeric paralmlroxybenzaldehydc, by the action of chloroform on an alkaline solution of phenol (Tiemann and Rcimcr, Ber. 1870, 824 ; Tiemann and Herzfeld, ibid. 1877, 63 and 213): C.H,-OH+CHCl3+4NaOH

=C,H«(ONa)CHO-t-3NaCl+3H2O. One part by weight of phenol, with 2 parts of caustic soda, is dissolved in at least 4 ]«irts of rater; the solution is heated to 50°-00° in a

flask fitted with a reflux condenser, and 2 parts of chloroform are gradually added, shaking continually. The colour of the liquid changes from yellow to deep red. The reaction is completed by boiling the mixture for half an hour, after which the excess of chloroform is distilled off. The liquid is then acidified with sulphuric acid and steam-distilled, when salicylaldehyde passe* over, along with unchanged phenol. The liquid remaining in the retort is filtered hot; on cooling, it deposits crystals of parahydroxybenzal- den3'de. The salicylaldehyde is separated from the phenol by shaking an ethereal solution of the two substances with hydrogen sodium sulphite, with which the salicylaldehyde forms a crystalline compound; this is separated, and decomposed by treatment with sodium carbonate or dilute sulphuric acid, when the aldehyde is liberated.

Salicylaldehyde is also formed when salicin C, SH1SO, is oxidised with a mixture of potassium diohromate and dilute sulphuric acid (Schiff. Annalen, 150, 193); and by the reduction of salicylic acid with sodium amalgam, or electro- lytically (H. Weil, Ber. 1908, 4147-4150).

Salieylaldehyde is manufactured by heating acetyl salicylic acid in an open vessel to 200°- 210° for 5 or 6 hours. The product is cooled, and boiled with several successive quantities of water. The residue is dissolved in 4 or 5 times its weight of acetone and poured into 20-30 volumes of water, when the aldehyde is precipitated in cheese-like flakes, which are then dried (Wetter, Eng. Pat. 20188, 1902). Liquid, with a pleasant aromatic odour. Solidifies at —20" in large crystals, and boils at 196-5°; sp.gr. 1-1731 at 13-5". Somewhat soluble in water, miscible in all proportions with alcohol or ether ; the aqueous solution gives a strong violet colouration with ferric chloride. By reduction it yields saligenin C,H4(OH)CHSOH : on oxidation, salicylic acid. When boiled with acetic anhydride and anhydrous sodium acetate it forms coumarin (q.v.). Forms salts with bases: thus C.H4(OK)CHO and C,H,(ONa)CHO; the alkali salts are not decomposed by carbon dioxide. With sulphuryl chloride it yields 5- chlorsalicylaldehyde (Peratoner, Gazz. chim. ital. 281, 235). Diiodosalicylaldehyde, mixed with a little monoidosalicylaldehyde, is obtained by treatment in dilute alcoholic solution with iodine and mercuric oxide (Seidel. J. pr. Chem. fii-l 57. 205). By warming together salioylaldehyde. phenol, glacial acetic acid, and concentrated sulphuric acid, Liebermann (Ber. 9, 801 ; 11, 1436) obtained hydroxy-aurin C,,H14O4, a violet- red colouring matter. Zulkowsky found, among the products of the same reaction, an orange colouring matter which he termed aurone, assigning to it the formula Cj,H,00,. Salicylaldehyde condenses with acetone and its derivatives in the presence of strong sulphuric acid, producing products which are converted on sulphonation into colouring matters which dve in shades from violet-red to blue-grey (D. R. P. 110520; Fabinyi, Chem. Zentr. 1900, ii. 3011 If the condensation is effected in the presence ot caustic soda di-o-oxydihenzalacetone results (D. R. P. 110521 ; Fabinyi, Chem. Zentr. 1900. ii. 302). E. Tummcley (Annalen, 251, 174-1871 has produced a large number of azo- condensation products."

Here's the second reference, made on p. 1194 in the Journal of Society of Chemical Industry (Great Britain):

Quote:

"Salicylide or Salicylic Aldehyde; Manufacture of.

J. Wetter. London. From F. Hoffmann la Roche and Co., Bale, Switzerland. Eng. Pat. 20,188, Aug. 7, 1902.

Aceto-salicylic acid is slowly heated in an open vessel to 200°—210° C. for five or six hours. The cooled product is boiled with successive quantities of water, and the residue dissolved in four or five times its weight of acetone. The clear acetone solution is poured into 20—30 times its volume of water, when tbe salicylide separates in cheese- like flakes, which are subsequently dried. — J. O. B.

For some reason these html versions of old photo-copied books on google are often loaded with typos (I've corrected them here). Guess it must have been typed hastily.

[Edited on 8/6/2009 by obsessed_chemist]

[Edited on 8/6/2009 by obsessed_chemist]

Nicodem - 6-8-2009 at 07:43

Quote:

Salieylaldehyde is manufactured by heating acetyl salicylic acid in an open vessel to 200°- 210° for 5 or 6 hours. The product is cooled, and boiled with several successive quantities of water. The residue is dissolved in 4 or 5 times its weight of acetone and poured into 20-30 volumes of water, when the aldehyde is precipitated in cheese-like flakes, which are then dried (Wetter, Eng. Pat. 20188, 1902).

Quote:

Obviously there is something wrong here. If both procedures are completely identical, like it is the case here, then it is not possible that one yields salicylaldehyde and the other salicylide. Since the first one which claims the product is salicylaldehyde, describes it as solid at room temperature, it is obvious this one is bullshit. The other describes a process at which conditions salicylic acid is known to give the poorly defined material known as "salicylide", then it is this one that it is more likely to be true, even though it starts from "aceto-salicylic acid" which could be either aspirin or something else.

Thanks for clarifying, Nicodem.

obsessed_chemist - 6-8-2009 at 09:08

Yeah, it seemed fishy to me from the beginning. I guess the mods could just delete this thread since it's kinda pointless. All of this fuss just over-analyzing a typo or two I found in 100+ yr. old literature. Hopefully no one else will make the same mistake.