Bisulfite

Heavy metals often can be removed effectively by chemical precipitation in the form of carbonates, hydroxides, or sulfides. Sodium carbonate, sodium bisulfite, sodium hydroxide, and calcium oxide are all used as precipitation agents. The solids precipitate as a floe containing a large amount of water in the structure. The precipitated solids need to be separated by thickening or filtration and recycled if possible. If recycling is not possible, then the solids are usually disposed of to a landfill. 

For years chemists have been using sodium bisulfite (that is BISULFITE not BISULFATE) to actually crystallize a ketone out of solution in order to separate it. As it so happens, our happy little MD-P2P is a ketone. And when an oil mixture containing it is mixed with a saturated solution of sodium bisulfite (NaHSOs) the MD-P2P crystallizes out as a bisulfite addition product . It can then be easily separated by filtration. Here s how it goes... 

When the MD-P2P/crap oil has been isolated and is at the point where one would normally apply distillation, this is the point where the chemist will use the bisulfite. One should not try this method unless the oil is rid of most solvent. In the Method 1 above, one would apply it after the ether from the final extraction has been removed by boiling or distillation (Yes, some distillation still ap-... 

Anyway, one has the P2P/crap oil, right Right. Next one makes a saturated sodium bisulfite solution by dissolving as much sodium bisulfite as will dissolve in a given amount of water (say, lOOOmL). Now one adds the MD-P2P oil into some of the saturated solution and stirs for 30 minutes. The temperature of the reaction will rise and a big old mass of P2P crystals will form. People often say that the crystals look like chicken fat. Those crystals formed because the bisulfite from the sodium bisulfite latched onto the ketone of the P2P to form a precipitate. And since the P2P is probably the only oil component with a ketone, it is gonna be the only thing of any consequence that crystallizes. 

The soiution is aliowed to cool and the crystals of the P2P-bisulfite addition compound are then separated by vacuum filtration, washed with a little clean dH20 then washed with a couple hundred mLs of ether, DCM or benzene. The filter cake of MD-P2P-bisulfate is processed by scraping the crystals into a flask and then 300mL of either 20% sodium carbonate solution or 10% HCi soiution are added (HCI works best). The soiution is stirred for another 30 minutes during which time the MD-P2P-bisulfite complex will be busted up and the P2P will return to its happy oil form. The P2P is then taken up with ether, dried and removed of the solvent to give pure MD-P2P. Whaddya think of that ... 

Strike sees a point to this in Vogel s text Practical Organic Chemistry (3 ed.)[37]. In it, Vogel crystallizes his ketones using a saturated sodium bisulfite solution that a/so contains a little solvent. This is in contrast to the straight up aqueous (only water) solution that Strike described above. Here is A/hat Vogel said on page 342 ... 

Prepare a saturated solutiotr of sodium bisulfite at the laboratory temperature from 40g of finely powdered sodium bisulphite about 70ml. of water are required. Measure the volume of the resulting solution and treat it with 70 per cent, of its volume of rectified spirit (or methylated spirit) [ethanol or methanol or both, dude] add sufficient water (about 45mL.) to just dissolve the precipitate which separates. ... 

Either pure aqueous or aqueous/solvent solutions work. It is entirely up to the preference of the chemist as to which one they use. Just to make one feel more secure, there is a little test one can do with the bisulfite solution to see if they got it right. Just put a little of that ketone known as acetone into the saturated solution and watch the crystals grow. Isn t it nice how chemistry works ... 

Now then, there are some chemists that rely on bisulfite as a tool to physically separate all of their ketone from an oil mix. But some chemists, using some methods, are rightfully sure enough that their ketones were produced in such high yields, and so cleanly, that separation isn t necessary at all. But even they, like anyone else, would still like to know for sure that what they made was P2P. This bisulfite procedure works in this regard as well. If one wants to know if what they made is P2P all one has to do is just drop a mL or so into the saturated bisulfite solution and see what happens. If crystals form, one has ketone. If not, one has fucked up. 

One final thought. Strike found that there are a lot of companies that do not sell sodium bisulfite (NaHSOa). In fact, a lot of companies list sodium bisulfite in their catalogs but tell the reader to see sodium metabisulfite instead because that is the only form of this compound they carry. In other words, a lot of companies sell sodium metabisulfite (NaaSaOs) as an acceptable alternative to the other. The Merck Index even says about sodium bisulfite that the [sodium] bisulfite of commerce consists chiefly of sodium metabisulfite, Nd2S20s, and for all practical purposes possesses the same properties as the true bisulfite". What this meant to Strike was that metabisulfite would work just as well. So some was purchased and tried. And it really does work just the samel... 

Of course the chemist may wish to forego purification and separation of the two remaining oils by distillation and opt for the sodium bisulfite procedure described earlier. That particular method is perfectly suited for this situation. Perfectly. 

So now we have this solvent containing ketone, dried with MgS04... Not being able to vac-distill today, took about 50 mis of solvent/ketone and placed in beaker on stir plate and boiled off the solvent. The resulting oil was a nice reddish-orange color. Had a very unique smell too. Took about 2 grams worth of this ail, added to a test tube containing a saturated solution of sodium bisulfite... In less than 60 seconds the oil precipitated into a whitish yellow mass (very similar to what acetone would do if added to a bisulfite solution). Never had this quick of a crystallization. Not... 

D. Now the ether will be a deep reddish yellow. Distill off the ether...quack...and take the temp up to 170 C to drive off any other volatiles. Should recover 90%+ of the original weight of oil. Now add 500 ml of saturated bisulfite and stir for 1.5 hours...Quack Vacuum Filter, the duck fat crystals Wash with water and ether, yield dull fine ppt in the filter cake...stable bisulfite addition product...can be stored forever...QuackU Yield -50 to 80% depending on a ducks technique ... 

Not-Strike may have seen. But what Dr. Quack did that SWINS did not was use the bisulfite test with positive results. What does that mean It means that some doublebonded oxygen was formed, unless Dr. Quack was fibbing to us, It cannot have been a propiophenone (don t ask) because propiophenones cannot form the bisulfite addition product. Could an aldehyde have formed (don t ask) Maybe. But highly unlikely considering the mechanism of the reaction. 

Although thiosulfate is one of the few reducing titrants not readily oxidized by contact with air, it is subject to a slow decomposition to bisulfite and elemental sulfur. When used over a period of several weeks, a solution of thiosulfate should be restandardized periodically. Several forms of bacteria are able to metabolize thiosulfate, which also can lead to a change in its concentration. This problem can be minimized by adding a preservative such as Hgl2 to the solution. 

Miscellaneous Reactions. Sodium bisulfite adds to acetaldehyde to form a white crystalline addition compound, insoluble in ethyl alcohol and ether. This bisulfite addition compound is frequendy used to isolate and purify acetaldehyde, which may be regenerated with dilute acid. Hydrocyanic acid adds to acetaldehyde in the presence of an alkaU catalyst to form cyanohydrin the cyanohydrin may also be prepared from sodium cyanide and the bisulfite addition compound. Acrylonittile [107-13-1] (qv) can be made from acetaldehyde and hydrocyanic acid by heating the cyanohydrin that is formed to 600—700°C (77). Alanine [302-72-7] can be prepared by the reaction of an ammonium salt and an alkaU metal cyanide with acetaldehyde this is a general method for the preparation of a-amino acids called the Strecker amino acids synthesis. Grignard reagents add readily to acetaldehyde, the final product being a secondary alcohol. Thioacetaldehyde [2765-04-0] is formed by reaction of acetaldehyde with hydrogen sulfide thioacetaldehyde polymerizes readily to the trimer. 

Acetaldehyde can be isolated and identified by the characteristic melting points of the crystalline compounds formed with hydrazines, semicarbazides, etc these derivatives of aldehydes can be separated by paper and column chromatography (104,113). Acetaldehyde has been separated quantitatively from other carbonyl compounds on an ion-exchange resin in the bisulfite form the aldehyde is then eluted from the column with a solution of sodium chloride (114). In larger quantities, acetaldehyde may be isolated by passing the vapor into ether, then saturating with dry ammonia acetaldehyde—ammonia crystallizes from the solution. Reactions with bisulfite, hydrazines, oximes, semicarb azides, and 5,5-dimethyl-1,3-cyclohexanedione [126-81 -8] (dimedone) have also been used to isolate acetaldehyde from various solutions. 

Specifications and Analytical Methods. The commercial material is specified as 97% minimum purity, determined by gas chromatography or acetylation. Moisture is specified at 0.05% maximum (Kad-Fischer titration). Formaldehyde content is determined by bisulfite titration. 

When aqueous solutions of sodium bisulfite are heated with butynediol, one or two moles add to the triple bond, forming sodium salts of sulfonic acids (61). 

Many of these reactions are reversible, and for the stronger nucleophiles they usually proceed the fastest. Typical examples are the addition of ammonia, amines, phosphines, and bisulfite. Alkaline conditions permit the addition of mercaptans, sulfides, ketones, nitroalkanes, and alcohols to acrylamide. Good examples of alcohol reactions are those involving polymeric alcohols such as poly(vinyl alcohol), cellulose, and starch. The alkaline conditions employed with these reactions result in partial hydrolysis of the amide, yielding mixed carbamojdethyl and carboxyethyl products. 

The reaction with sodium sulfite or bisulfite (5,11) to yield sodium-P-sulfopropionamide [19298-89-6] (C3H7N04S-Na) is very useful since it can be used as a scavenger for acrylamide monomer. The reaction proceeds very rapidly even at room temperature, and the product has low toxicity. Reactions with phosphines and phosphine oxides have been studied (12), and the products are potentially useful because of thek fire retardant properties. Reactions with sulfide and dithiocarbamates proceed readily but have no appHcations (5). However, the reaction with mercaptide ions has been used for analytical purposes (13)). Water reacts with the amide group (5) to form hydrolysis products, and other hydroxy compounds, such as alcohols and phenols, react readily to form ether compounds. Primary aUphatic alcohols are the most reactive and the reactions are compHcated by partial hydrolysis of the amide groups by any water present. 

Sulfomethylation. The reaction of formaldehyde and sodium bisulfite [7631-90-5] with polyacrylamide under alkaline conditions to produce sulfomethylated polyacrylamides has been known for many years (44—46). A more recent pubHcation (47) suggests, however, that the expected sulfomethyl substitution is not obtained under the previously described strongly alkaline conditions of pH 10—12. This C-nmr study indicates that hydrolysis of polyacrylamide occurs and the resulting ammonia reacts with the NaHSO and formaldehyde. A recent patent claims a new high pressure, high temperature process at slightly acid pH for preparation of sulfomethylated polyacrylamide (48). 

In a typical adiabatic polymerization, approximately 20 wt % aqueous acrylamide is charged into a stainless steel reactor equipped with agitation, condenser, and cooling jacket or coils. To initiate the polymerization, an aqueous solution of sodium bisulfite [7631-90-5] is added, followed by the addition of a solution of ammonium persulfate [7727-54-0] N2HgS20g. As the polymerization proceeds, the temperature rises to about 90°C, and then begins to fall at the end of the polymerization. The molecular weight obtained depends primarily on the initiator concentration employed. 

Isothermal polymerizations are carried out in thin films so that heat removal is efficient. In a typical isothermal polymerization, aqueous acrylamide is sparged with nitrogen for 1 h at 25°C and EDTA (C2QH2 N20g) is then added to complex the copper inhibitor. Polymerization can then be initiated as above with the ammonium persulfate—sodium bisulfite redox couple. The batch temperature is allowed to rise slowly to 40°C and is then cooled to maintain the temperature at 40°C. The polymerization is complete after several hours, at which time additional sodium bisulfite is added to reduce residual acrylamide. 

Chemical assay is preferably performed by gas—hquid chromatography (glc) or by the conventional methods for determination of unsaturation such as bromination or addition of mercaptan, sodium bisulfite, or mercuric acetate. 

Analogously, aldehydes react with ammonia [7664-41-7] or primary amines to form Schiff bases. Subsequent reduction produces a new amine. The addition of hydrogen cyanide [74-90-8] sodium bisulfite [7631-90-5] amines, alcohols, or thiols to the carbonyl group usually requires the presence of a catalyst to assist in reaching the desired equilibrium product. 

Isolate. A relatively pure chemical produced from natural raw materials by physical means, eg, distillation, extraction, crystallization, etc, and therefore natural or by chemical means, ie, via hydrolysis, bisulfite addition products, and regeneration, etc, and therefore artificial by 1993 U.S. labeling regulations. 

Nature Identical Flavor Matenal A flavor ingredient obtained by synthesis, or isolated from natural products through chemical processes, chemically identical to the substance present in a natural product and intended for human consumption either processed or not eg, citral obtained by chemical synthesis or from oil of lemongrass through a bisulfite addition compound. 

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