628 HASLAM, WHETTEM A S D SOPPET: THE DETERMISATION OF [Vol. 76 The Determination of Methyl a-Chloro-acr yla te in the Atmosphere BY J. HASLAM, S. M. A. WHETTEM ASD W. W. SOPPET Colorimetric and volumetric methods have been devised for the deter- mination of methyl a-chloro-acrylate in the atmosphere. The colorimetric method, which is suitable for the range of concentrations 0.5 to 25 mg of methyl a-chloro-acrylate per cubic metre of air (0.1 to 5 p.p.m. v/v at 20" C and 760 mm pressure), is based on the passage of a known volume of the atmosphere through 0.00 1 N potassium permanganate solution. The colour of the resulting solution is compared either with that of standards prepared from known amounts of methyl a-chloro-acrylate in 0.00 1 h- potassium permanganate solution or with standard colour discs in a Lovibond comparator.The volumetric method, which is suitable for the range 25 to 100 mg of methyl a-chloro-acrylate per cubic metre of air (5 to 20 p.p.m. v/v at 20" C and 760 mm pressure), is based on the passage of a known volume of the atmosphere through 0.02 N potassium permanganate solution and determination of the volume of potassium permanganate consumed, by addition of an excess of 0.02 N potassium oxalate solution and titration of the excess of potassium oxalate with 0-02 N potassium permanganate solution. THE production of the new polymer poly-methyl a-chloro-acrylate necessitated a rapid and accurate method for the determination of small concentrations of methyl a-chloro-acrj.latc in the atmosphere. I t was hoped that the method ultimately worked out would be simple and capable of rapid application on a plant engaged in the manufacture of the polymer.PRELIMISARY EXPERIMENTS ON THE ABSORPTION OF METHYL a-CHLORO-ACRYLATE BY POTASSIUM PERMASCANATE SOLUTION I t was known that methyl a-chloro-acrylate reacted readily with aqueous potassium permanganate solution and preliminary tests were performed to find out whether advantage could be taken of this reaction in working out a suitable method. In these preliminary experiments about 0.03 g (accurately weighed) of methyl a-chloro-acrylate was placed on glass wool contained in a small stoppered flask. This flask was connected to two jet bubblers, each containing 25 ml of 0.1 N potassium permanganate solution, which were connected to a Rotameter and suction pump.Air was aspirated through the apparatus for 10 minutes at the rate of 1 litre per minute. By weighing the flasks before and after the aeration it was shown that the methyl a-chloro-acrylate was completely removed in the air stream. After aeration the bubblers were disconnected, and 20 ml of 20 per cent. v/v sulphuric acid solution and 25 ml of 0.1 N potassium oxalate solution were added to each. The decolorised solutions were washed out into two 250-ml flasks and heated to 80" C, after which the excess of oxalate was titrated with 0.1 N potassium permanganate solution. In these experiments the absorption of methyl a-chloro-acrylate by potassium perman- ganate solution was very efficient. For examplc, in one experiment the volume of potassium permanganate solution consumed in the first bubbler was 17-05 ml, whereas in the second bubbler but 0.3 ml of 0.1 N potassium permanganate was consumed.Duplicate tests were in good agreement and indicated that 1.46 mg and 1.50 mg of methyl a-chloro-acrylate required 1 ml of 0.1 N potassium permanganate. DEVELOPMEXT OF A VOLUMETRIC METHOD- I t was considered that the concentration of the vapours in the atmosphere of a plant might be in the range of 25 to 100mg of methyl a-chloro-acrylate per cubic metre of air, i.e., 5 to 20 p.p.m. v/v at 20" C. Further, it was thought that a practical test should not involve the passage of the suspected atmosphere through permanganate solution for longer than 15 minutes. This would involve the absorption of amounts of methyl a-chloro-acrylate of the order of only 0-5 to 2-Omg.On consideration of these factors further experimentsSov., 19511 METHYL a-CHLORO-ACRYLATE I 5 THE ATMOSPHERE 629 were carried out with a weaker permanganate solution, 15 ml of 0.02 N potassium perman- ganate solution being placed in each bubbler. In this second set of experiments an amount of methyl a-chloro-acrylate within the range of 0.5 to 2.0 mg was first weighed out accurately in a stoppered micro weighing bottle. The stopper was removed and the bottle and stopper dropped into a 100-ml flask. The flask, preceded by an Arnold bubbler containing 0.01 N potassium permanganate, which served as a guard tube, was connected immediately to the absorption train. The absorption train (Fig. 1) consisted of two jet bubblers, each containing 15ml of 0.02 N potassium permanganate solution, a Rotameter and pump, all connected in series.The flask containing the sample was immersed in a bath of water at 50" C and air was aspirated through the apparatus at the rate of 1.5 litres per minute, the temperature of the water being gradually raised to 80" C. To each .4t the end of 15 minutes the air was turned off. Air intake I for of flow Fig. 1 . -4bsorption train for the determination of methyl a-chloracrylate in the atmosphere of the bubblers 5 ml of 10 per cent. v/v sulphuric acid and then 20 ml of 0.02 N potassium oxalate solution were added and the contents of the bubblers were allowed to stand until the permanganate became decolorised. The contents of each bubbler were then washed into 250-ml conical flasks with water and heated to 80" C, after which the excess of potassium oxalate was titrated with 0.02 N potassium permanganate solution.A blank determination was made by measuring 15 ml of 0.02 N potassium permanganate solution into another flask, adding 5 ml of 10 per cent. v/v sulphuric acid, 20 ml of 0.02 N potassium oxalate solution and titrating the excess of potassium oxalate with 0.02 N potassium permanganate solution at 80" C as before. The results indicated that the absorption of the vapours within the range considered, 25 to 100 mg of methyl a-chloro-acrylate per cubic metre of air, was efficient when judged by the small amount of permanganate consumed in the second bubbler; e.g., in one experiment the volume of 0-02 N permanganate solution consumed in the first bubbler was 6.0 ml and in the second bubbler it was 0.4 ml.Duplicate tests were in good agreement and indicated that 0.285 mg of methJ.1 a-chloro-acrylate required 1 ml of 0.02 N potassium permanganate solution. Confirmation that the absorption of methyl a-chloro-acrylate by 0-02 N potassium permanganate solution under the above conditions is accompanied by complete ionisation of the chlorine of the chloro-acrylate was given by the following experiment. After aeration of 0.487 mg of methyl a-chloro-acrylate, the contents of the permanganate bubblers were transferred to a beaker and diluted to 30 ml with distilled water. To this was added 1 ml of concentrated nitric acid, A.R., and then N hydrogen peroxide solution until the perman- ganate solution was just decolorised. The excess of hydrogen peroxide was removed by boiling, and the solution was allowed to cool and was then diluted to 50 ml with water.To630 HASLAM, WHETTEM ASD SOPPET: THE DETERMIXATION OF [Vol. 76 the dilute solution 1 ml of a 5 per cent. w/v solution of silver nitrate, A.R., was added, and after 5 minutes the turbidity was compared with previously prepared permanent “Perspes” standards.1 The turbidity of these standards corresponded with those obtained on addition of 1 ml of the 5 per cent. w/v solution of silver nitrate to 50 ml of a solution containing a known amount of 0.01 N hydrochloric acid and 1 ml of nitric acid, A.R. The turbidity comparison was performed against a background of black matt filter-paper.These experiments indicated that the turbidiity obtained in the experiment of 0-487 mg of methyl a-chloro-acrylate, containing 0.143 mg (of chlorine, matched that of the permanent standard prepared from 0.4 ml of 0.01 N hydrochloric acid, containing 0-142 mg of chlorine. The volumetric method was satisfactory for the range of concentrations considered, i e . , from 25 to 100 mg of methyl a-chloro-acrylate per cubic metre of air, and could un- doubtedly be extended to the determination of smaller concentrations by the passage of larger volumes of air. Xevertheless, the passage of larger volumes of air would involve an increase in the time taken for the test beyond the desired maximum of 15 minutes. Certain observations that had been made on the effect of adding increasing amounts of methyl a-chloro-acrylate solution to the same volume of potassium permanganate solution suggested that the colours produced might be used in a colorimetric test, particularly if the permanganate solution was relatively weak.A standard solution of methyl a-chloro-acrylate in water was prepared as follows. /4 0.25-ml portion of methyl a-chloro-acrg-late was shaken in a graduated flask with 500 ml of water at room temperature and the solution was filtered. To 10ml of this solution were added 40 ml of 0.02 N potassium permanganate solution. The mixture was well shaken, 10 ml of 10 per cent. v p sulphuric acid and 50 irnl of 0-02 N potassium oxalate were added and the excess was titrated with 0.02 N potassium permanganate solution as described on p.629. On the basis of previous experiments, which had indicated that 1 ml of 0.02 N potassium permanganate was equivalent to 0.285 mg of methyl a-chloro-acrylate, it was shown that the filtered solution contained 0.17 g of methyl a-chloro-acrylate per 500 ml. This solubility figure of 0.034 per cent. w/v may be useful in other work. A standard solution of methyl a-chloro-acrylate in water was then prepared by diluting 5.85 ml of the strong solution, i.e., 2.0 mg of methyl a-chloro-acrylate, to 100 ml with water. One millilitre of this standard solution contained 0.02 mg of methyl a-chloro-acrylate. Colour calibrations were made by taking 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0 and 5-0 ml of this standard solution of methyl a-chloro-acrylate, diluting each to 5.0 ml with water and adding to each 5.0 ml of 0.002 N potassium permanganate solution.Reaction with the permanganate took place immediately and the colours that developed ranged from red through orange - red to orange - yellow as the concentration of methyl a-chloro-acrylate increased. The Lovibond colour values of these solutions were measured in a Lovibond tintometer with 1-cm cells, and readings are shown in Tab1.e I. DEVELOPMENT OF A COLORIMETRIC METHOE- Experiments were therefore performed to test this. TABLE I COLOURS PREPARED BY THE REACTIObi OF METHYL E-CHLORO-ACRYLATE ON 5 ml OF 0.002 N POTASSIUM: PERMASGANATE SOLUTION Volume of standard solution, ml 0.5 1.0 1-5 9.0 2.5 3.0 4-0 5.0 Weight of methyl r or-chloro-acr ylate, mg 0.01 0.02 0.03 0.04 0.05 0-06 0.08 0.10 Lovibond colour values Red Yellow A 7 4.5 4.1 3.9 3.7 3.6 3.4 2.9 2.4 0.0 0-3 1.1 2.7 3.1 4.2 6.6 8.5 To obtain some information about the reproducibility of the test and the stability of the colours, standards corresponding to 0.05 mg and 0-10 mg of methyl a-chloro-acrylateNov., 19511 METHYL a-CHLORO-ACRYLATE IN THE ATMOSPHERE 631 were prepared on successive days.The Lovibond colour values of these standards were determined 10 minutes and 3 hours after preparation. The results are shown in Table 11, from which it was concluded that a satisfactory colorimetric method could be based on examination of the coloured reaction products of methyl a-chloro-acrylate and potassium permanganate after colour development for 5 minutes. TABLE I1 EFFECT OF TIME ON THE COLOURS PREPARED BY THE METHYL a-CHLORO- ACRYLATE - POTASSIUM PERMANGANATE REACTION Lovibond colour values Weight of I A > Volume of methyl After 10 minutes After 3 hours standard ot-chloro- & & solution, acrylate, Red Yellow Red Yellow 2-5 0.05 3.3 3.1 3.3 5.6 5.0 0.10 2.2 8.9 2.5 9.2 ml "g 2.5 0.05 3.3 3.1 3-0 5.0 5.0 0.10 2.0 8.5 3.1 8.9 Attention was next directed to the efficiency of absorption of methyl a-chloro-acrylate vapour by weak solutions of potassium permanganate.To set up a known weak concentration of methyl a-chloro-acrylate vapour, in order to check the efficiency of the absorption of the vapour in very weak solutions, would be a matter of some difficulty. Instead of doing this, an experiment was made with an unknown concentration, which was then determined by the volumetric method with 0.02 N potassium permanganate solution and by the colorimetric method, 0.001 N potassium permanganate solution being used for the absorption.The concentration of methyl a-chloro-acrylate vapour in the laboratory fume cupboard, which contained chloro-acrylate residues in an open vessel, was used for the experiment. A point was chosen for the tests, and for the colorimetric method air was drawn at the rate of 1-5 litres per minute through two jet bubblers each containing 10 ml of 0-001 N potassium permanganate solution. After 3 minutes the potassium permanganate solution in the first bubbler had changed colour appreciably and the test was stopped. A range of standards containing from 0.0 to 0.10 mg of methyl a-chloro-acrylate by O*Ol-ml steps was prepared as before and the colours of the sample bubblers were matched against the standards.The first bubbler was equivalent to the 0.06-mg standard and the second was equivalent to the 0.02-mg standard, i.e., 4.5 litres of air contained 0.08 mg of methyl a-chloro-acrylate. Hence the concentration was calculated as 18mg of methyl a-chloro-acrylate per cubic metre of air. The air was tested at the same point by the volumetric method. Again air was drawn at the rate of 1.5 litres per minute through two jet bubblers, each containing 15 ml of 0.02 N potassium permanganate, for 15 minutes. The total permanganate consumed amounted to 1.6 ml of 0.02 N potassium permanganate solution, which is equivalent to 0.456 mg of methyl a-chloro-acrylate, i.e., 22.5 litres of air contained 0.456 mg of methyl a-chloro-acrylate.From this the concentration was calculated as 20 mg of methyl a-chloro-acrylate per cubic metre of air. The close agreement between these results was sufficient evidence that the methyl a-chloro-acrylate vapour was completely absorbed by 0.001 N potassium permanganate solution in the method described. It was concluded from these results that a colorimetric method based on the procedure used in the above experiments would be suitable for the determination of concentrations of methyl a-chloro-acrylate in air ranging from 0.5 to 25 mg per cubic metre (0.1 to 5 p.p.m. v/v) by absorbing the vapours in 0.001 N potassium per- manganate solution at the rate of 1.5 litres per minute over periods ranging from 3 to 16 minutes.Initially it was proposed that the colour matching should be made against standards prepared in the laboratory by interaction of known volumes of potassium permanganate solution with known amounts of methyl a-chloro-acrylate solution. I t was realised, however, that much time would be saved if a colour disc suitable for use in a Lovibond comparator could be obtained, The co-operation of Mr. Chamberlin of The Tintometer Ltd. was sought,632 HASLAM, WHETTEM AND SOPPET: 1HE DETERMINATION OF [Vol. 76 and a satisfactory colour disc was made. I t consists of nine individual coloured glasses that have been prepared to match the colours obtained by the interaction of 10 ml of 0.001 N potassium permanganate solution and the following amounts of methyl a-chloro-acrylate : 0.00, 0.01, 0.02, 0.03, 0.04, 0.05, 0-06, 0.08 and 0.10 mg.I t is necessary to view the test solution in the 13.5-mm comparator cells 5 minutes after colour development, the screen provided being used on the sample side. Full details of the colorimetric method are given below. The method includes a description of both procedures, ie., that using standards prepared in the laboratory from known amounts of methyl a-chloro-acrylate and permanganate, and that using the Lovibond comparator. Although it is probable that most of the problems that arise will be dealt with satis- factorily by the colorimetric procedure, it may be necessary on occasions to determine very high concentrations of the order of 25 to 100 mg of methyl a-chloro-acrylate per cubic metre of air, For this reason the volumetric procedure is also given after the colorimetric method.COLORIMETRIC METHOD APPARATUS- Jet bubblers-Two of these are required. Their dimensions are: length, 26 cm; internal diameter, 22 mm; tube diameter, 6.5 mm, drawn out to 1 to 1-5 mm at the tip (see Fig. 1). Rotameter-This is calibrated to measure rates of flow from 1.5 to 0.1 litres per minute a t 20" C and a pressure of 760 mm of mercury. REAGENTS- Potassium permanganate solutions, 0.02 N , 0.002 N and 0.001 N . Potassium oxalate solution, 0.02 N . Sulphuric acid, 10 per cent. v / v . Standard solzition of methyl a-chloro-acrylate in water (1 ml = 0.02 mg)-Prepare the standard aqueous solution of methyl a-chloro-acrylate as follows.Measure from a I-ml graduated pipette 0.25 ml of methyl a-chloro-acrylate into a 500-ml measuring flask. Dilute with water to 500ml and shake well. Filter into a dry flask and transfer, by means of a pipette, 10 ml of the filtered solution to a 250-ml conical flask. Add 40 ml of 0.02 N potassium permanganate solution, shake well and add 10 ml of 10 per cent. v/v sulphuric acid and then 50 ml of 0.02 N potassium oxalate solution from a pipette. When the solution has decolorised, heat it to 80" C and titrate the excess of potassium oxalate with 0.02 N potassium per- manganate solution. From the volume of 0.02 N potassium permanganate consumed, calculate the strength of this solution as milligrams of methyl a-chloro-acrylate per millilitre of solution. 1 ml of 0.02 N potassium permanganate = 0,285 mg of methyl a-chloro-acrylate. Measure from a burette, reading to 0.01 ml, an amount of this standardised solution equivalent to 2-0mg of methyl a-chloro-acrylate into a 100-ml graduated flask and dilute to 100 ml with water.This is the standard solution used in the colour comparison, and 1 ml of it contains 0.02 mg of methyl a-chloro-acrylate. SAMPLING PROCEDURE- Measure 10 ml of 0.001 N potassium permanganate solution into each of the two jet bubblers and connect these in series to the Rotameter and suction pump (Fig. 1). Aspirate the air to be tested through the apparatus at the rate of 1.5 litres per minute until the colour of the permanganate solution in the first bubbler appears to be satisfactory for colour com- parison (usually 3 to 15 minutes).Stop the air flow and drain the solutions from each bubbler carefully into 50-ml Nessler cylinders. Note the volume of air passed. COLOtlR COMPARISON- While the aeration through the permanganate is proceeding, prepare methyl a-chloro- acrylate colour standards as follows. Into nine Nessler cylinders measure, by means of a graduated pipette, the following amounts of the standard solution of methyl a-chloro- acrylate: 0.0, 0.5, 1.0, 1-5, 2.0, 2-5, 3.0, 4.0 and 5.0 ml. Dilute each solution to 5.0 ml with water and add 5.0 ml of the 0.002 N potassium permanganate solution. Visually match the colours of the permanganate solutions from the test with the prepared standards. Com- bine the two results and calculate the final result to milligrams of methyl a-chloro-acrylate per cubic metre of air sampled.Nov., 19511 METHYL a-CHLORO-ACRYLATE IN THE ATMOSPHERE 633 RAPID COLORIMETRIC METHOD WITH THE LOVIBOND COMPARATOR- Drain the contents of the first bubbler into one of the 13.5-mm glass comparator cells and fill the other comparator cell with water.Place the cells in the comparator so that the colour glasses of the methyl a-chloro- acrylate colour disc cover the water cell. See that the screen supplied with the disc is in position covering the sample cell and rotate the disc until the colours of the sample solution and colour disc match. Read the value shown on the disc, which represents milligrams of methyl a-chloro-acrylate in the 10 ml of 0.001 N potassium permanganate solution. Match the colour of the solution in the second bubbler in the same way.Combine the two results and calculate the final result to milligrams of methyl a-chloro- acrylate per cubic metre of air sampled. Carry out the sampling procedure described above. VOLUMETRIC METHOD APPAriATCs- As for the colorimetric method. REAGEKTS- Potassium permanganate solution, 0.02 N. Potassium oxalate solution, 0.02 N . Sulphuric acid, 10 per cent. v / v . PROCEDURE- Measure 15 ml of 0.02 N potassium permanganate solution into each of the two jet bubblers and connect these in series to the Rotameter and suction pump (Fig. 1). Aspirate the air to be tested through the apparatus at the rate of 1-5 litres per minute for 15 minutes. Add 10 ml of 10 per cent. v/v sulphuric acid and 20 ml of 0.02 N potassium oxalate solution and allow to stand until the permanganate is decolorised.Wash out each bubbler separately into 250-ml conical flasks. Titrate the excess of oxalate with 0.02 N potassium permanganate solution after heating the contents of each flask to 80" C. Carry out a blank titration by measuring 15 ml of 0.02 N potassium permanganate solution into another flask, adding 10 ml of 10 per cent. v/v sulphuric acid, 20 ml of 0.02 N potassium oxalate solution and titrating the excess of oxalate with 0.02 N potassium permanganate solution as before. Calculate the volume of 0-02 N potassium permanganate solution con- sumed in each bubbler by subtracting the blank titration from the sample titration. The total permanganate consumed is the sum of these two figures.The total volume in millilitres of 0.02 N potassium permanganate consumed multiplied by 0.285 gives the weight in milligrams of methyl a-chloro-acrylate in the volume of air passed. Calculate the result to milligrams of methyl a-chloro-acrylate per cubic metre of air. APPLICATION OF THE COLORIMETRIC METHOD TO THE DETERMINATION OF METHYL A test was carried out by the colorimetric method on the atmosphere inside a fume chamber . An open beaker containing 6 g of methyl a-chloro-acrylate was placed inside the chamber and the ventilating fan was switched on. The two jet bubblers containing the 0.001 N potassium permanganate solution were set up inside the fume chamber so that the air intake was 15 inches vertically above the beaker. This height corresponded approximately to mouth level.Air was aspirated through the bubblers at the rate of 1 litre per minute. While this was in progress the colour standards were prepared in 50-ml Nessler cylinders. The air flow was stopped after 30 minutes and the permanganate solutions were drained from the bubblers into two similar 60-ml Nessler cylinders. RESULTS- a-CHLORO-ACRYLATE IK THE ATMOSPHERE I N A FUME CHAMBER Rate of flow of air = 1 litre per minute. Time for which air was aspirated = 30 minutes. Volume of air aspirated = 30 litres. On matching the colour of the solution from the first bubbler against the standards, it was found to be between the 0.03 and O-OPmg standard and was estimated to be 0.033 mg634 HASLAM, WHETTEM AND SOPPET [Vol. 76 of methyl a-chloro-acrylate.The solution from the second bubbler matched the 0-O-mg standard and therefore contained no methyl a-chloro-acrylate. Hence 30 litres of air contained 0.033 mg of methyl a-chloro-acrylate and 1000 litres of air contained 1.10 mg of methyl cr-chloro-acrylate, i e . , the concentration was 1.1 mg of methyl a-chloro-acrylate per cubic metre of air, or 0.22 p.p.m. v/v at 20" C and 760 mm pressure of mercury. THE EFFECT OF METHYL METHACRYLATE ON THE COLORIMETRIC METHOD Two sets of standards were prepared in 10 ml of 0.001 N potassium permanganate solution, one set containing 0.02, 0.04, 0.06, 0.08 and 0-10 mg of methyl a-chloro-acrylate and the other set containing the same weights of methyl methacrylate. The methyl a-chloro- acrylate standards were normal, i.e., their colours ranged from permanganate tint to orange - yellow with increasing amounts of chloro-acrylate. The methyl methacrylate standards, however, all retained the permanganate tint, the intensity of which diminished with increasing amounts of methacrylate. Tests were also carried out on known amounts of methyl a-chloro-acrylate with and with- out added amounts of methyl methacrylate. As a result of these tests it is our opinion that 4 parts by weight of methyl methacrylate have the same effect on the chloro-acrylate test as 1 part of methyl a-chloro-acrylate. In other words if, for example, the atmosphere contained 4mg per cubic metre of methyl a-chloro-acrylate and 4mg per cubic metre of methyl methacrylate, the application of the colorimetric method to this atmosphere would give a result of 6 mg per cubic metre of methyl a-chloro-acrylate. This method for determining the lachrymatory methyl a-chloro-acrylate is designed for use on a plant producing it, where contamination of the atmosphere would be due entirely or almost entirely to the ester. If used in other circumstances, positive results in the test would not necessarily be indicative of the ester without confirmatory evidence. Incidentally, we have shown that methyl a-chloro-acrylate reacts extremely rapidly with weak potassium permanganate solution at concentrations in which such substances as ethyl alcohol and form- aldehyde have a negligible effect. REFERENCE The behaviour of the two sets of standards was quite different. 1. Haslam, J., and Squirrell, D. C. M., Biochem. J., 1951, 48, 48. IMPERIAL CHEMICAL INDUSTRIES LIMITED PLASTICS DIVISION WELWYN GARDEN CITY, HERTS. May, 1961