Sciencemadness Discussion Board

Sodium acetate discoloration

Cat_got_my_tungsten! - 23-9-2007 at 00:32

Sodium acetate having been heated via stovetop/teflon pan to remove water from what was formerly a solution of sodium bicarbonate and 5% distilled white vinegar, had towards the very end of dehydration turned a yellow hue. This happened cheifly to the hydrated salt under the dry salt losing the last bit of the water. NaHCO3 in bottom of pan, CH3CO-OH added until no more reaction was observed. -> then boiled till dryness. My query is what caused the discoloration? This was not apparent with other salts I have seen elsewhere.

P.S. Rubber spatula to stir while in solution, wooden spatula to scrape from pan.

YT2095 - 23-9-2007 at 01:14

a lot of food grade vinegars have sugars in them too.

Fleaker - 23-9-2007 at 09:20

If it wasn't distilled white vinegar or glacial acetic, then that might be why you got that color-the sugars were probably caramelizing.

guy - 23-9-2007 at 10:54

I got the same problem using distilled vinegar too.

garage chemist - 23-9-2007 at 11:13

Sodium acetateis not truly anhydrous until the solidified salt has been melted (ca. 330°C)- you need to do this to your product, else reactions calling for anhydrous sodium acetate will fail.
The dehydration and melting can cause discoloration even with reasonably pure chemicals. This is no cause for concern.

chemkid - 23-9-2007 at 11:16

When i was working with sodium acetate mine melted to a brown syrupy liquid. I presume the color is from impurities (also using vinegar and baking soda) but my question is will this liquid once cooled turn back into crystals or just harden to a blob in my beaker?

Chemkid

Ozone - 23-9-2007 at 11:23

Was your teflon coated pan *perfectly* clean? If not even traces of adhered material will cause the discoloration. Caramelization of sugars too (nevermind what might happen with traces of protein).

Does anyone know about how much iron might be present in vinegar? I would do the test (o-phenantholine), but I must finish mowing the lawn in the infernal heat in crawfish town (and I noticed that my o-phenanthroline reagent has turned brown, which means I have to obtain and make more:P).

Traces (that is, even ppm) of iron have cause me to have problems with the acquisition of totally white crystalline products.

Nevermind oxidation...

Cheers,

O3

Cat_got_my_tungsten! - 23-9-2007 at 11:50

Fantastic, thanks for the great suggestions. I have 1-bromo-3-chloro-5,5-dimethyl hydantoin lying around and through my past experiments I have found that isopropyl alchohol effectively liberates what i am assuming to be Br2 & Cl2. Then the hot, brominated solution of Isoproplyl alcohol goes from reddish bromine color to clear. Could this mean that the bromine/chlorine has replaced either the hydroxyl group or one of the hydrogens? After leaving it set i see that the soulution had crystallized. Now if it had produced isopropyl bromide, the sodium acetate would then hypothetically produce isopropyl acetate and sodium bromide. I am concerned though that having all that dissolved hydantoin in the solution would create some sort of a problem. Would this be practical to expect somthing along these lines?

chloric1 - 24-9-2007 at 02:06

I might be srong but---the hydantoins they use for spas are fairly insoluble substances. I do know that the bromine and chlorine are loosely bound and are probably consumed in the reaction. The crystaline deposit is more than likely dimethylhydantoin. Look up the solubility in CRC Handbook or Lange.

It is very doubtful that you have any isopropyl bromide as your halogen compound is a powerful oxidizer. Does the liquid in question have a stinging eye burning odor? It may be a complex mixture of chloro & bromo acetones:o

You need a reducing proton acceptor to get alkyl halides like Dimethyl Formamide if you want to use halogenated cyclonitrogen compounds.:(

not_important - 24-9-2007 at 02:31

Quote:
Volatile components in the vapors of natural and distilled vinegars were identified by gas chromatography by comparing their retention dumes with compounds of known composition and by functional group analysis. Twenty-five volatile components were identified from three natural vinegars (cider, 19 components; wine, 17 components; tarragon, 20 components), and 11 volatile components were identified from five samples of distilled vinegar. Four components were present in all vinegars tested: acetaldehyde, acetone, ethyl acetate, and ethyl alcohol. The natural vinegars had the largest number of volatile components. This was attributed to the nature of the fermentable carbohydrate material used for production of the alcohol subsequently used for vinegar manufacture (e.g. apples and grapes). The importance of the earbonyls, alcohols, and esters to vinegar flavor is discussed.


http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-2621...

MagicJigPipe - 28-9-2007 at 00:06

I tried the vinegar/bicarbonate reaction in a "clean environment" with distilled white vinegar. Then I boiled the solution to dryness. I got a mixture of about 50% pure white NaCH3COO and 50% off-white to dark brown colored, syrupy (some of it crystalline though) goo. I thought, well maybe this was the normal discoloration that garage chemist mentioned. So, I dissolved it in a little bit of distilled water to see if it would be clear but it turned dark brown.

So, I concluded that even in distilled vinegar there appears to be sugar of some sort (the brown NaCH3COO had a slightly sweet vinegar smell). Unless the acetate decomposed but I'm pretty sure I didn't reach that temp.

Sauron, I request that you do not reply to this unless you are going to remain objective and not speak condescendingly to me.

not_important - 28-9-2007 at 00:53

I don't think it is sugars in the distilled white vinegar, sugars are just not that volatile. I think it is aldehydes and ketones condensing into gorp.

From the times I've played with this, you get less discolouration if you let the solution evaporate and room temperature or slightly above, maybe helped by pulling a vacuum on the solution. The brown colouration is soluble in isopropyl alcohol, acetone and MEK, and ether; this suggests compounds with low ratios of hydroxy groups - condensed unsaturated compounds.

If you kept under 150 C the acetate shouldn't have decomposed, SFAIK.

MagicJigPipe - 28-9-2007 at 21:43

You know what. I never thought of that. And I know that sugars won't distill over but I have no idea of the manufacturing process and thought they might add some in the process. I just got done letting some NaAcetate solution evaporate and there is no discoloration but it seems to only dry to a certain point and then remain wet. I'll try using a dessicant and/or a vacuum.

[Edited on 28-9-2007 by MagicJigPipe]

MagicJigPipe - 8-12-2007 at 12:10

I did a little reading since my last post and discovered that some "distilled" vinegars don't actually mean that they distilled the actual vinegar but the ethanol used to make it.

I'm not sure of the commercial process most often used to oxidize the EtOH but I know one of them is the bacteria method.

Also, there is something called "mother of vinegar" that forms in old bottles of vinegar which is a brown goo of acetic acid bacteria and cellulose.

Could heating vinegar speed up it's formation?

[Edited on 8-12-2007 by MagicJigPipe]

MagicJigPipe - 12-12-2007 at 01:35

Ok, this time I used generic vinegar (Kroger brand) instead of the Heinz brand and I only used a pint of vinegar in a 8x8 pan. I heated at 176*C until it was about a cm from the bottom of pan. Then I took out the hot saturated solution, let it cool and let the NaAc crystals form. Then I put it back in and heated at 135*C for a few more hours while stirring the crystals around occasionally. I got very little discoloration. Light yellow instead of dark brown. That's the way I'll do it from now on.

And the hot saturated solution wasn't brown like usual. It was light milky white.

US to Metric
8x8 = 20.32cmx20.32cm
pint = 473.176475mL

*EDIT*

Dissolving in water and vacuum filtering seems to remove some gunk. Almost too much trouble for such a cheap substance.

[Edited on 12-12-2007 by MagicJigPipe]

MagicJigPipe - 18-4-2008 at 19:51

Okay, I figured out what the brown sticky crap probably is. This guy wrote an article on the production of vinegar and it's true--"distilled" white vingegar means the EtOH used to create the acetic acid is distilled, not the vinegar itself. He seems to know what he is talking about.

http://www.nowheat.com/fooddb/food/vinegar2.htm

In the quote below he is talking about what the "distilled" vinegar is likely to contain as far as "nutrients" go:

"The nutrient mixture is said to consist of a variety of salts and some carbon and nitrogen sources such as glucose, citric acid, ammonium phosphate, some yeast extract or dried yeast, and hydrolyzed soy flour. At the conclusion of the fermentation the vinegar is not distilled, but rather is filtered to remove microorganisms and particulate material and diluted to bring the acetic acid level down from values as high as 15 to 20% to roughly 5%."

My guess would be the glucose is causing the brown discoloration. What do you guys think?

EDIT
By the way, about the above post, after heating the solution to dryness the same gunky brown crap was obtained. Just less brown and "gunky".

[Edited on 4-18-2008 by MagicJigPipe]

16MillionEyes - 20-4-2008 at 20:10

I'm so glad someone posted information about this, I'm familiar with the brownish sodium acetate from white vinegar and sodium bicarbonate. The best and by far more effective method of obtaining the pure acetate is to distill the vinegar (best twice) and then reacting it. Since I lack the proper equipment to do so I've gone the straight way and it's afforded me a painful purification process for the acetate. Until now, after careful crystallization and gravity filtration (I have no way of doing vacuum filtration) I get a nice white powder; half a gram so far from like 30-40 grams (I don't have a balance either, I'm such a great chemist...).

copperastic - 30-3-2014 at 11:08

That happened to me to. Is there any way to remove the sugar?

Etaoin Shrdlu - 30-3-2014 at 11:29

Try crystallizing, washing with isopropyl alcohol, then recrystallizing.

Brain&Force - 30-3-2014 at 16:00

I think the problem may also be the source of baking soda - some "fridge scrubbers" have an air freshener in them as well. There may be a reaction between one of the organics in each chemical. But this depends on the source of baking soda. The culprit is usually Arm & Hammer.

S.C. Wack - 30-3-2014 at 16:32

Arm & Hammer is USP grade. It's the vinegar. Do not boil anywhere near dry, lower the heat, be cautious. Etaoin Shrdlu's advice, though I don't recall now what solvent I used. There are likely several other threads where it's all been said.

Brain&Force - 30-3-2014 at 18:03

There's one variant for odor scrubbing that contains an air freshening compound, but their all-purpose baking soda is perfectly fine.