Sulfuryl chloride

Sulfuryl chloride

Sulfuryl chloride is an inorganic compound with the formula SO₂Cl₂. At room temperature, it is a colorless liquid with a pungent odor. Sulfuryl chloride is not found in nature, as can be inferred from its rapid hydrolysis.

Sulfuryl chloride is commonly confused with thionyl chloride, SOCl₂. The properties of these two sulfur oxychlorides are quite different: sulfuryl chloride is a source of chlorine whereas thionyl chloride is a source of chloride ions. An alternative IUPAC name is sulfuroyl dichloride.

Sulfur is tetrahedral in SO₂Cl₂, being bound to two oxygen atoms via double bonds and to two chlorine atoms via single bonds. The oxidation state of the sulfur atom is +6, as in H₂SO₄.

Synthesis

SO₂ + Cl₂ à SO₂Cl₂

SO₂Cl₂ is prepared by the reaction of sulfur dioxide and chlorine in the presence of a catalyst, such as activated carbon.  The crude product can be purified by fractional distillation. It is uncommon to prepare SO₂Cl₂ in the laboratory because it is commercially available. Sulfuryl chloride can also be considered a derivative of sulfuric acid.

Reactions

Sulfuryl chloride reacts with water, releasing hydrogen chloride gas and sulfuric acid:

2 H₂O + SO₂Cl₂ à 2 HCl + H₂SO₄

SO₂Cl₂ will also decompose when heated to or above 100 °C, about 30 °C above its boiling point.  Upon standing, SO₂Cl₂ decomposes to sulfur dioxide and chlorine, which gives the older samples a slightly yellowish color.

Uses

Sulfuryl Chloride is the Sulfuric oxychloride where as sulfinyl chloride is the sulfurous oxychloride. Sulfuryl Chloride is a colorless to yellowish liquid with a pungent odor. It boils at 69°C, decomposed by hot water and alkalies; soluble in most organic solvents (benzene, chloroform, carbon tetrachloride and acetic acid). It is not found in nature due to strong hydrolysis. It is explosive also with donor solvents such as alcohols, ethers, DMSO and DMF. It decompose at its boiling point. It has two S-Cl single bonds and two S=O solid bonds. It is prepared by the reaction of sulfur dioxide and chlorine in the presence of activated carbon. It is used as a solvent and as a source of chlorine in chemical reactions. Sulfuryl chloride is useful mainly in preparing pesticides. It is used as a chlorinating (and sulfochlorinating) agent of alcohols, alkyls, aromatics, and epoxides for the target molecules of pharmaceuticals, disinfectants, dyestuffs, rayon, and poison gases. Chlorination in organic synthesis with sulfuryl chloride is more selective than elementary chlorine. It is useful to avoid secondary reactions. Chlorination of alcohols to yield alkyl chloride.

Sulfuryl chloride is often used as a source of Cl₂. Because it is a pourable liquid, it is considered more convenient than Cl₂ to measure, store, and dispense. SO₂Cl₂ is widely used as a reagent in the conversion of C-H → C-Cl adjacent to activating substituents such as carbonyls and sulfoxides. It also chlorinates alkanes, alkenes, alkynes, aromatics, and epoxides. Such reactions occur under free radical conditions using an initiator such as AIBN.

Overall reaction

C₄H₉Cl + SO₂Cl₂+AIBNàC₄H₈Cl₂ + SO₂ + HCl

Below side reaction possible if there is more amount of sulfuryl chloride.

It can also be used to convert disulfides into their corresponding sulfenyl chlorides. SO₂Cl₂ can also convert alcohols to alkyl chlorides. In industry, sulfuryl chloride is most used in producing pesticides.

SO₂Cl₂ can also be used to treat wool to prevent shrinking.

Precautions

SO₂Cl₂ is toxic, corrosive, and acts as a lachrymator. As described above, it can form explosive mixtures with water, as well as donor solvents such as DMSO and DMF.

Selenium dioxide

Selenium dioxide (SeO₂)

Selenium dioxide (SeO₂) is an important reagent in organic syntheses, as it is both an oxidant and weakly acidic.  Selenium dioxide is the chemical compound with the formula SeO₂. This colorless solid is one of the most frequently encountered compounds of selenium.  The solid sublimes readily. The vapor has an odor resembling horseradish sauce and can burn the nose and throat on inhalation.  SeO₂ is considered an acidic oxide: it dissolves in water to form selenous (selenious) acid. Often the terms selenous acid and selenium dioxide are used interchangeably. It reacts with base to form selenite salts containing the SeO2−3 anion. For example, reaction with sodium hydroxide produces sodium selenite:

SeO₂ + 2 NaOH → Na₂SeO₃ + H2O

Uses in Organic synthesis:

SeO₂ is an important reagent in organic synthesis. Oxidation of paraldehyde (acetaldehyde trimer) with SeO₂ gives glyoxal and the oxidation of cyclohexanone gives cyclohexane-1,2-dione. The selenium starting material is reduced to selenium, and precipitates as a red amorphous solid which can easily be filtered off. This type of reaction is called a Riley oxidation. It is also renowned as a reagent for "allylic" oxidation, a reaction that entails the conversion

R₂C=CR'-CHR"₂ + [O] → R₂C=CR'-C(OH)R"₂

(where R, R', R" are alkyl or aryl).

Mechanism of oxidation

Procedures:

A 500-ml three-necked, round-bottomed flask is fitted with a mechanical stirrer, a thermometer, a dropping funnel, and a reflux condenser. A solution of 0.74 g. (0.0067 mole) of selenium dioxide in 150 ml. of tert-butyl alcohol is introduced into the flask, followed by 68 g. (0.50 mole) of β-pinene. The resulting mixture is warmed to 40 °C with a hot water bath before 35 ml. (0.62 mole) of 50% aqueous hydrogen peroxide is added drop wise over 90 minutes, during which time the mixture is maintained at 40–50 °C by occasional immersion in a cold water bath. After stirring for an additional 2 hours, the reaction mixture is diluted with 50 ml. of benzene, washed with three 50-ml. portions of saturated aqueous ammonium sulfate, and dried over sodium sulfate. A small amount of hydroquinone is added, and the solvents are removed on a rotary evaporator. trans-Pinocarveol is isolated by simple distillation under reduced pressure, yielding 37–42 g. (49–55%), b.p. 60–70° (1 mm.).

Procedure was taken from Organic Syntheses, Coll. Vol. 6, p.946 (1988); Vol. 56, p.25 (1977).

 --------------------------------------------------------------------------------------------

1,2-Cyclohexanedione. A 3-l. round-bottomed flask, fitted with stirrer and dropping funnel, is placed in a water bath containing a coppercoil through which cooling water may be circulated. In the 3-l. flask is placed 1708 g. (17.4 moles, 1.8 l) of cyclohexanone. Tap water is circulated through the cooling coil, and a solution containing 387 g. (3 moles) of selenious acid (H₂SeO₃), 500 ml. of 1,4-dioxane, and 100 ml. of water is added drop wise and with stirring to the cyclohexanone over a period of 3 hours. The reaction mixture immediately turns yellow, and red amorphous selenium gradually appears. Stirring is continued for 5 additional hours at water-bath temperatures and then for 6 more hours at room temperature. Removal of the bulky, amorphous selenium is accomplished with the aid of a 6-in. Buchner funnel. The selenium is returned to the reaction flask and extracted with 300 ml. of boiling 95% ethanol for 1 hour. The solution, obtained by decantation from the compact gray selenium, is combined with the above filtrate in a 4-l. distilling flask. Distillation under reduced pressure gives two fractions. The lower-boiling fraction (25–60°/16 mm.) consists mainly of ethanol, water, dioxane, and cyclohexanone; the higher-boiling one (60–90°/16 mm.) contains cyclohexanone and 1,2-cyclohexanedione with traces of water and dioxane. The yield of crude product is approximately 322 g.

Procedure was taken from Organic Syntheses, Coll. Vol. 4, p.229 (1963); Vol. 32, p.35 (1952).

 --------------------------------------------------------------------------------------------

Microwave-assisted selenium dioxide mediated selective oxidation of 1-tetralones to 1,2-naphthoquinones

This is a microwave reaction reported in Tetrahedron Letters Volume 50, Issue 1, 7 January 2009, Pages 39-40

 --------------------------------------------------------------------------------------------

Tips: 

1. Since only catalytic quantities of selenium dioxide are required, the danger of handling large quantities of this material is avoided.
2. Formation of selenium and organoselenides commonly arise in oxidations using molar quantities of selenium dioxide, are not encountered.
3. If too much selenous acid is added at once, or the cooling discontinued, the solution will heat up and the reaction will become extremely vigorous with subsequent decrease in yield.
4. Selenium compounds are exceedingly toxic 

Butyl lithium titration and estimation

Titration of butyllithium (nBuLi or secondary Butyl lithium or tert-Butyl lithium)

Butyl lithiums are usually delivered in “sure seal” bottles which allow using them without contamination by oxygen and moisture. However, frequent use of these bottles damages the septa which can result in decomposition of the compound therefore butyllithium (and other stock alkyllithiums) must be titrated regularly. Many methods are available for this purpose; however, some of the most reliable procedures are given below.

1^st Method:  This method employs 1,3-diphenylacetone p-tosylhydrazone (see Shapiro et al. J. Organomet. Chem. 1980, 186 (2), 155-158) as the reactive agent because of its ability to give persistent color upon anion formation.  Cool a solution of  291 mg (0.769 mmol) hydrazone in 8 mL anhydrous THF under Argon to 0 ^oC and slowly add BuLi via a accurate 2mL syringe (1-2 mL of butyl lithium in syringe should be fine).  During tritration (ice bath): curls of deep yellow will surround each drop of added BuLi, and then dissipate.  At the end-point: persistent (deep) yellow color will be observed.  If you add too much of BuLi ypu will observe deep red color (high concentration of dianion).

Strength of Butyl lithium = (mmol of hydrazone / volume of butyl lithium added)

2^nd Method:  This is GILMAN Double Titration (J. Organomet. Chem. 1964, 2, 447 – 454.) method and a very old method.  It is preferred over single titration methods because it not only gives the concentration of the solution but also provides an indication of the quality of the organolithium.  To determine the total content of base, an aliquot (usually 0.50 to 1.5 ml, depending on the expected concentration) of the solution of the organolithium is quenched with 20 ml of water. The resulting solution of LiOH is titrated with a solution of standardised hydrochloric acid using phenolphthalein as the indicator. To determine the residual content of base of the organolithium, an aliquot (preferably the same amount as before) of the organolithium is reacted with 1,2-dibromoethane as follows: 0.20 ml of dry 1,2-dibromoethane (BE CAREFUL: CARCENOGENIC) are dissolved in 3 ml of dry DEE in an inert atmosphere. The organolithium is added dropwise with vigorous stirring. After 5 min of stirring, the solution is diliuted with 20 ml of water and then titrated as described above. 1,2-Dibromethane reacts with organolithiums as follows:

This procedure destroys the organolithium without producing LiOH, so that the difference of the two titrations gives the exact concentration of the organolithium. A typicale example is given below:

I. A 0.50 ml aliquot of a solution of n-BuLi in hexanes was quenched with water, treated with a few drops of a phenolphthalein solution in water/methanol and titrated with standardised hydrochloric acid unitil complete disappereance of the pink color. When titrating highly flammable organometallics such as t-BuLi, step I should be carried out with degassed water under nitrogen.

II. A second 0.50 ml aliquot was quenched with dibromoethane as described above. After 5 min of stirring, the mixture was diluted with water and after addition of the indicator titrated (with vigorous stirring – it is a biphasic system).

c(HCl) = 0.1034 N; V(HCl)I = 7.90 ml; V(HCl)II = 0.25 ml.

V(HCl)eff = V(HCl)I – V(HCl)II = 7.90 ml – 0.25 ml = 7.65 ml

c(n-BuLi) = [V(HCl)eff x c(HCl)] / V(aliquot) = [7.65 ml x 0.1034 mmol ml-1] / 0.50 ml =

1.58 M

Residual base = [0.25 ml / 7.90 ml] x 100 % = 3.2 %. This value is typical for a high quality organolithium. If the content of residual base is higher than ~ 10 % of the total content of base, the quality of the organolithium is poor, which may be detrimental to very sensitive reactions.

3rd Method: Dry THF (10 mL) is added using a syringe, followed by 2-butanol (0.500 mL, measured as accurately as possible using your 1 mL syringe). Allow the solution to cool for 5 minutes. As accurately as possible, draw 5.00 mL of n-butyl lithium in hexanes from the reagent bottle using 10 mL syringe. (Caution: n-butyl lithium is extremely corrosive and can ignite spontaneously in air. Respect it !!!.) Add the butyl lithium to the solution drop wise, noting when the first rust-red color appears and persists (this is your first endpoint). Once you have persistent color, add the remainder of the butyl lithium to the flask. Immediately rinse your syringe twice with hexane and expel the washings into an open beaker in the hood before cleaning the syringe out with water and acetone (Otherwise, your needle will choke by the formation of lithium hydroxides and carbonates). Next, back titrate the butyl lithium in the flask with 2-butanol until the rust red color is just extinguished (this is your second endpoint). This should be done immediately as the indicator is not stable and will degrade over time. 

Calculate the concentration of the butyllithium solution from both the forward and back titrations and compare these values to the stated value on the bottle. Assume that one mole of butyllithium reacts with one mole of 2-butanol to form the corresponding lithium alkoxide. For tert-BuLi and sec-BuLi you may want to use ether as a solvent and have it ice cooled because these react with THF at room temperature quite fast.

TLC stains for amines

 

First of all if it has got an aryl then it should be UV active otherwise you can use Ninhydrin stain. It works best for amino acids, amines, amino sugars.  Spray the plate with a solution of 0.2g ninhydrin in 100ml ethanol and heat until spots (reddish) appear.  You can achieve better sensitivity if you add 3 ml of acetic acid to the above solution. You can also add 1 g of cadmium acetate (for detection of heterocyclic amines) or 1ml of pyridine (for detection of peptides) in combination with AcOH.

Alternatively you can spray the plate with a solution of tert-Bu-hypochlorite in CCl4 and then dry it to get rid of all the hypocholite (otherwise whole plate stains black and it will be difficult to visualize) and the spray it with a m,m'-dimethoxybenzidine.  Amines and amides which have free NH give a black spot on a white back ground.  Another stain which you can use is Ehrlich’s reagent (very good for amines, indoles, pyrrolizidine alkaloids).  This reagent is nothing but a combination of p-Dimethylaminobenzaldehyde and hydrochloric acid reagent just spray the plate with a solution of 1 g of p-dimethylbenzaldehyde in 75 ml of MeOH and 50 ml of concentrated HCl and gently heat the plates.

Vanillin reagent will also detect amines and amino acids.  6 g Vanillin,1.5 ml Conc. sulfuric acid, 95 ml 96% Ethanol.  Dip the plates and heat it for the spots to appear.  Some PIP stain (potassium iodoplatinate stain) 1 g hexachloroplatinate (alfa), 20 g KI, 592 ml H₂O, 54 ml conc. HCl.  You can heat the plate high for spots to appear (not so good!) leave the plate at rt the spots appear very good but this is again a slow process.

Chemistry Interview

Insider tips!!!

Want to know what turns on and off recruiters, then you are at the right place.  I have put down some points which I recollected from my experiences.  The first thing you got to remember is that there is a concern behind every question the interviewer asks for.  In most of the companies recruiters who interview chemists and chemical engineers at all levels are look to find candidates who can exhibit technical mastery, show passion, communicate clearly and work well in teams.  Recruiters try to zero down on some of some of the important characteristics of chemists by asking questions such as: Can you tell me about your research (present a clear and concise description of their current research project)? How would you describe your strengths and weaknesses? Describe a time when you have demonstrated your leadership skills. Tell me what you like or don't like about your supervisor.

Interviews are job seekers' best chance to showcase their qualifications in the best possible light but it is good for candidates to cite any of their accomplishments at the end which were not mentioned earlier.  Make sure that you don’t promote yourself excessively like putting up a show of your awards, rewards, certificates in chemistry (you can include all these in your resume).

Now that we have seen some ways when recruiters turn on now we will see what are some of the ways of turning off recruiters during an interview? an arrogant attitude and stretching the truth to sell yourself do not work well, recruiters say. Don’t overstep and know your boundaries.

What if you getting nervous to attend an interview? Take a deep breath and let it out slowly, relax. Look at your interviewer in the eyes and greet him by name (if you know it) combined with a affable handshake and a pleasant smile, and say, "I'm glad to meet you. How are you today?”  All this starts off a good beginning.

Don’t be friendly with recruiters be professional. Recruiters are not there to make friends or to engage in gusty conversation with the candidate. Their main task is to weed out people out, and narrowing the field to a few.  Recruiters first examine a candidate's technical and communication skills set to evaluate whether the candidate has the capacity to do the work or not. Then they look at leadership skills, motivation, ability to set goals and achieve, if the candidate will succeed on the job.  Coming to the term leadership don’t get confused by it.  Suppose something good happened while you were in that position so tell them as a individual what difference did you make so that it happened.

Recruiters refer to technical, communication, and fit as the deciding factor and they assign the rating differently. Appearance and communication skills are important only to a point and chemists are not highly trained lab technicians but they can think on their own.

Some of the recruiters do homework for each interview by gaining some knowledge up on the candidate's research field. That way he can ask critical questions about the science and go beyond the questions which can be answered with ease. They ask candidates why they approached their research in a certain way and challenge them to look at the same problem using alternate solutions. A honest "I'm not sure" answer is not taken negatively.

Hope i helped you to some extent!