Ferric chlorides

The highly charged transition metals have a marked tendency to form complexes. The ferric ion, Fe. is one for which numerous studies have been done in an attempt to define its complexing behavior with anions such as hydroxyl, cyanide, bromide and chloride. The complexes occurring between ferric and chloride ions will be discussed here. 

Early estimates of the first association constant were made in the 1930 s by Bray and Hershey (F2) and MoUer (F8) using potentiometric measurements. In 1942, Rabinowitch and Stockmayer (F9) presented the results of their spectroscopic study under controlled acidity, temperature and ionic strengths. From their results they calculated estimates of the first three association constants  

While they note that there is evidence of at least one more complex in concentrated chloride solutions, FeCll, they chose not to consider it. Their calculations Included a term to compensate for the association of ferric and hydroxyl ions, even though this term is small due to the low hydroxyl concentration, The results, in which they felt only could be considered as dose to exact are  

The constant 1.51 is the log of the association constant at 26.7 0 extrapolated back to Infinite dilution (K° = 32.). Using this equation, they calculated values for log K at temperatures from 20 to 50 C which were then plotted versus 1/T. From its slope, a value for the heat of association was determined. Values for G° and AS of the reaction were derived using the value of 30 for Kf at 25 C. The results presented are  

Gamlen and Jordan (F6) used spectrophometric measurements to determine K3 and the next association constant  

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A fiowsheet for this part of the vinyl chloride process is shown in Fig. 10.5. The reactants, ethylene and chlorine, dissolve in circulating liquid dichloroethane and react in solution to form more dichloroethane. Temperature is maintained between 45 and 65°C, and a small amount of ferric chloride is present to catalyze the reaction. The reaction generates considerable heat. 

In early designs, the reaction heat typically was removed by cooling water. Crude dichloroethane was withdrawn from the reactor as a liquid, acid-washed to remove ferric chloride, then neutralized with dilute caustic, and purified by distillation. The material used for separation of the ferric chloride can be recycled up to a point, but a purge must be done. This creates waste streams contaminated with chlorinated hydrocarbons which must be treated prior to disposal. 

The problem with the fiowsheet shown in Fig. 10.5 is that the ferric chloride catalyst is carried from the reactor with the product. This is separated by washing. If a reactor design can be found that prevents the ferric chloride leaving the reactor, the effluent problems created by the washing and neutralization are avoided. Because the ferric chloride is nonvolatile, one way to do this would be to allow the heat of reaction to raise the reaction mixture to the boiling point and remove the product as a vapor, leaving the ferric chloride in the reactor. Unfortunately, if the reaction mixture is allowed to boil, there are two problems ... 

Anhydrous cupric sulphate is white but forms a blue hydrate and a blue aqueous solution. The solution turns yellow when treated with concentrated hydrochloric acid, dark blue with ammonia, and gives a white precipitate and brown solution when treated with potassium iodide. A yellow-brown aqueous solution of ferric chloride becomes paler on acidification with sulphuric or nitric... 

Both these acids are colourless, but the spots of each acid on a filter-paper strip show up in ultraviolet light as intense blue fluorescent zones. They can also be detected, but considerably less sensitively, by spraying with ethanolic ferric chloride solution, which gives with N-methylanthranilic acid a purple-brown coloration. 

Finally spray the paper with neutral 1% ethanolic ferric chloride solution the methylanthranilic acid spot develops a purple-brown coloration, whereas the anthranilic acid gives only a very faint pink coloration. 

Reactions of Aspirin, (i) Distinction from Salicylic acid. Shake up with water in two clean test-tubes a few crystals of a) salicylic acid, (0) aspirin, a very dilute aqueous solution of each substance being thus obtained. Note that the addition of i drop of ferric chloride solution to (a) gives an immediate purple coloration, due to the free —OH group, whereas (b) gives no coloration if the aspirin is pure. 

Dissolve a small portion of the sodium derivative in a few mi. of water in a test-tube, and add one drop of ferric chloride solution. A deep red coloration is produced, but rapidly disappears as the iron is precipitated as ferric hydroxide. The sodium (derivative (A) of the nitromethane wh dissolved in water undergoes partial hydrolysis,... 

Reactions and colorations with ferric chloride solution. 

Ferric chloride solution is then added to com ert the sodium ferrocyanide to the deep blue ferric ferrocyanide (or Prussian Blue), dilute sulphuric acid being also added to dissolve any ferrous and ferric hydroxides present in the other-... 

Add about 0 2 g. of ferrous sulphate crystals to the first portion of the filtrate contained in a boiling-tube. An immediate dark greenish-grey precipitate of ferrous hydroxide should occur if the mixture remains clear, add a few ml. of sodium hydroxide solution. Now boil the mixture gently for a few minutes to ensure formation of the ferrocyanide, cool under the tap, add one drop of ferric chloride solution, and then acidify... 

Section 7. Reactions and colorations with aqueous Ferric Chloride solution. 

Ferric chloride solution sometimes contains a large excess of HCl which would interfere with the following reactions. If it is very markedly acidic add dil. NaOH solution, drop by drop, to the ferric chloride solution until a small but permanent precipitate of ferric hydroxide is obtained. Filter this off through a small fluted filter paper, and use the clear filtrate. The latter is still not quite neutral owing to hydrolysis, but this feeble acidity does not interfere with the tests given below. 

Colorations or coloured precipitates are frequently given by the reaction of ferric chloride solution with.(i) solutions of neutral salts of acids, (ii) phenols and many of their derivatives, (iii) a few amines. If a free acid is under investigation it must first be neutralised as follows Place about 01 g. of the acid in a boiling-tube and add a slight excess of ammonia solution, i,e., until the solution is just alkaline to litmus-paper. Add a piece of unglazed porcelain and boil until the odour of ammonia is completely removed, and then cool. To the solution so obtained add a few drops of the "neutralised ferric chloride solution. Perform this test with the following acids and note the result ... 

Take two test-tubes A and B in A place about 5 ml. of neutralised tartaric acid solution and in B place 5 ml. of distilled water. To each solution add 3-4 drops of ferric chloride solution. Place a piece of white paper under the tubes, look down their length and note that A is definitely yellow compared with the control tube B. This yellow colour is given by a-hydroxy-carboxylic-acids, lactic acid, tartaric acid, citric acid. 

Dissolve a few crystals of phenol in water and add ferric chloride solution a violet coloration is produced. Repeat, using i 2 drops of m-cresol shaken up with about i ml. of water a violet coloration is again produced. Catechol (in dilute solution) gives a green coloration. 

Dissolve 2 3 drops of o toluidine in a few drops of dil. HCl and add 2 3 drops of ferric chloride solution a green coloration is produced and is slowly replaced by a bluish-green or blue precipitate. 

Unless all the excess of ammonia has been driven off in the preparation of the neutral salt, the result obtained on adding ferric chloride will be misleading owing to the precipitation of ferric hydroxide. If this is suspected, the tests should be repeated using an aqueous solution of the pure sodium salts of these acids for comparison. 

Ferric chloride coloration. Add a few drops of FeClj solution to a few drops of the aldehyde an intense violet coloration is produced, a. Does not restore the colour to Schiff s reagent. 

The neutral salts of many acids treated with ferric chloride give colorations or precipitates. 

Ferric chloride reaction. For the success of this reaction it is important that the solution should be neutral. Excess of acid usually inhibits the production of colour or precipitate, and excess of alkali gives a reddish-brown precipitate of ferric hydroxide. A neutral solution may be made as follows ... 

Esters form hydroxamic acids which give colorations with ferric chloride. 

Hydroxamic acid formation cf. Section 9, p. 334). To a few drops of an ester, add 0 2 g. of hydroxylamine hydrochloride and about 5 ml. of 10% NaOH solution and gently boil the mixture for 1-2 minutes. Cool and acidify with dil. HCl and then add a few drops of ferric chloride solution. A violet or deep red-brown colour develops immediately. 

Aqueous solutions give with ferric chloride the characteristic reactions of the neutral salt of the acid (p. 348). Identify the carboxylic acids by the tests already given (Section 14, p. 347), or by the preparation of one of the crystalline derivatives below. 

Aqueous solutions (when obtainable) give no reaction with ferric chloride. This is an important distinction from ammonium salts (sec above). Salicylamide, being also a phenol, is however an exception (p. 344). 

Ferric chloride coloration. To a trace of the solid add ferric chloride solution and shake an intense violet coloration is produced, owing to the presence of the ohenolic grouping. 

Ferric chloride coloration. Add FeCl, solution to a few crystals (or to an aqueous solution) of /> nitrophenol a violet-red coloration is produced. o-Nitrophenol does not give a coloration. 

J. Treat with neutral ferric chloride solution (p. 332). 

L. Treat with hydroxylamine and ferric chloride (pp. 334, 353). Violet or red colorations given particularly by esters. Deep colorations also given by acid chlorides, acid anhydrides and by some acid amides (usually aliphatic) and by a few of the simpler anilides. 

Salicin is a colourless crystalline substance, soluble in water. It does not reduce Fehling s solution nor does it give a coloration with ferric chloride. On hydrolysis with emulsin, glucose and salicyl alcohol are produced the former reduces Fehling s solution and the latter gives a violet coloration with ferric chloride. 

Cool the remainder of the filtrate and extract three times with ether, using 20 - 30 ml. for each extraction. Dry the combined ethereal extracts over powdered anhydrous sodium sulphate. Filter into a small flask and distil off the ether on a water-bath. Pour the residual oil into a small dish or beaker crystallisation takes place almost immediately. The salicyl alcohol so obtained is almost pure, but it may, if so desired, be recrystallised from a small quantity of benzene. It is a colourless crystalline solid, m.p. 86 , readily soluble in water it gives a violet coloration with ferric chloride. 

Ferric Chloride. Approx. 4 5%. Dissolve 75 ml. of " liquid FeCl, in water and make up to i litre. Alternatively, dissolve 75 g. of FeCls,6H20 in water, add 10 ml. of cone. HCl, and make up to i litre. 

The alkylidene dimethone (dimedone) (I) upon boiling with glacial acetic acid, acetic anhydride, hydrochloric acid and other reagents frequently loses water and passes into a substituted octahydroxanthene or the anhydride (II), which often serves as another derivative. The derivatives (I) are soluble in dilute alkali and the resulting solutions give colourations with ferric chloride solution on the other hand, the anhydrides (II) are insoluble in dilute alkali and hence can easily be distinguished from the alkylidene dimedones (I). 

P Keto esters (t.g., ethyl ocetoacetate) are soluble in solutions of caustic alkalis but not in sodium carbonate solution. They give colours with freshly prepared ferric chloride solution a little alcohol should be added to bring the ester into solution. Sodium ethoxide solution reacts to yield sodio compounds, which usually crystallise out in the cold. Phenylhydrazine yields pyrazolones. They are hydrolysed by boiling sulphuric acid to the Corresponding ketones, which can be identified as usual (Section 111,74). 

The enol form is thus temporarily removed from the solution and the ferric chloride colouration produced by the enol form consequently disappears and the solution becomes colourless. Some of the unchanged keto form of the ester then passes into the enol form in order to restore the original equilibrium and the ferric chloride colouration therefore reappears. 

Other catalysts which may be used in the Friedel - Crafts alkylation reaction include ferric chloride, antimony pentachloride, zirconium tetrachloride, boron trifluoride, zinc chloride and hydrogen fluoride but these are generally not so effective in academic laboratories. The alkylating agents include alkyl halides, alcohols and olefines. 

In an alternative procedure 26 g. of anhydrous ferric chloride replace the aluniiniuni chloride, the mixture is cooled to 10°, and the 50 g. of tert.-butyl chloride is added. The mixture is slowly warmed to 25° and maintained at this temperature until no more hydrogen chloride is evolved. The reaction mixture is then washed with dilute hydrochloric acid and with water, dried and fractionally distilled. The yield of tert.-butyl benzene, b.p. 167- 170°, is 60 g. 

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