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Analysis of Pure Compounds Containing Carbon, Hydrogen, and Oxygen, with and without Halogens

Organic Substances

I. Analysis of Pure Compounds Containing Carbon, Hydrogen, and Oxygen, with and without Halogens

W . R . K i r n e r , Coal R esearch Laboratory, Carnegie In stitu te o f T ech n ology, P ittsb u rgh , Pa.

A direct sim ultaneous micromelhod has been de­

veloped fo r the determ ination o f carbon, hydrogen, an d oxygen in compounds containing these elements alone or with chlorine an d bromine also present.

Ten substances have been analyzed, the mean precision o f the oxygen determ ination being about 0.3 to 0 / t p er c e n t The precision of the oxygen determination is lim ited by the degree o f precision obtainable in the carbon-hydrogen determ ination, a n y errors in the determ ination of the latter being m u ltiplied by rather large factors. The oxygen

consumed during the combustion is determ ined gasom etrically with considerable precision.

The results of previou s investigators using sim ila r macro- or sem i-micromethods have been critically an alyzed an d the discovery m ade that the apparen tly satisfactory results obtained by them were largely due to com pensation of errors o f con­

siderable m agnitude.

The investigation is being continued on more complex com pounds an d w ill fin a lly be extended lo the an a lysis o f coal an d its products.

T

H E lack of a satisfactory method for the direct deter­

mination of oxygen in organic substances and the potential value of such a method as a control on all of the other determinations made on a substance are generally recognized. Oxygen continues, however, to be almost uni­

versally calculated “ by difference,” despite th e fact th a t this calculation involves, especially in complex substances, the summation of errors made in the determ ination of the in­

dividual components.

The published methods for the direct determ ination of oxygen m ay be grouped into the following five classes:

1. Complete oxidation of the substance by means of an inorganic oxidizing agent, followed by a determination of the amount of oxidant consumed (Table I).

Ta b l e I . De t e r m i n a t io n o p Ox y g e n Us in g In o r g a n i c Ox i d i z i n g Ag e n t s

El em ents Pr e sen t

Inorganic in Compounds

Author Ox id izin g Ag ent Studied

G ay-Lussac a n d T h e n a rd (I S ) K C lO i C, H , O, N

von B aum hauer (1) CuO C, H , O

Stromeyer® (27) CuO-NasCO» C, H , 0 , N , S, Cl

M aum ene* (16) PbO-Ca»(PO«)t ...

Ladenburg (15) AglOa-HiSO« C, H , O

yon B aum hauer (2) CuO -A glO i C. II, O, N

M itscherlich* (19) HgO C, H , O, N , S, P, and

. . halogens

P helps? (21) C hrom ic acid-H ,S04 C, H .O , N

Boswell (5) CuO -asbestos C, H , O

Strebm ger« (26) K I0*-H iS04 C, H , O, S, N . and halogens S ta n ik and N em es/ (14) K I0 » -H ,S 0 , C. H , 0 , S. N S tanilc a n d N em ew ( is ) K I0 i- H ,S 0 . C, H , 0 . S, N, and

halogens a D eterm ined only oxygen consum ed. N o t applicable to n itro com pounds or n itrates. R esults alw ays low.

f> N o d a ta given.

c Technic very complex and tedious.

N itrogen com pound stu d ied gave th e poorest result.

* N o t applicable to nitrogen com pounds which yield poor results on kjeldahlization—i. e., nitro-, a*o-, and heterocyclic com pounds, hydrazones, osazones, etc.

/ A m icrom ethod. H as sam e lim itations as cited in su b scrip t • plus halogens. Oxygen calculated b y difference. Oxygen consum ed determ ined directly. H ydrogen calculated b y m eans of involved equations.

a Same as su b scrip t / except difficulty due to halogens removed,

2. Destructive catalytic hydrogenation of the substance, followed by a determination of all resulting oxygen-containing substances (Table II).

Ta b l e I I . De t e r m i n a t i o n o f Ox y g e n b y Hy d r o g e n a t i o n Au t h o r

W anklyn and Frank® (28) Boswell*» (6)

te r M eulen c (IS) S chuster^ (23)

D o l r h a n d W i l l * (

El e m e n t s Pr e s e n ti n Co m p o u n d s St u d i e d

C, H , O C, H , O, N , S, and halogens

C, H, O, and coal C. H , 0 C, H , O, and coal C, H , O, N , S, an d fuels Dolch and Will* (S)

te r M eulen/ (17) v an Beek and de W ard* (3) Will A (29)

Russell an d Fulton* (22) C, H , O

° N o d a ta given.

& Five ab so rp tio n tubes used requiring te n weighings. Slow. N o t applicable to com pounds containing less th a n 30 to 40 p e r c en t of oxygen nor to com pounds which yield easily condensable reduction products.

c A sem i-m icrom ethod. T he m ost com plete stu d y on th e d eterm ination of oxygen y e t m ade. Som ew hat complex w hen several elem ents are present besides carbon, hydrogen, an d oxygen.

d C onfirm ation of te r M eulen m ethod applied to pure com pounds, b u t a criticism of m ethod when used for analysis of coal.

9 C riticism of te r M eulen m ethod.

/ R eply to S chuster a n d to Dolch an d W ill.

0 T estim onial for te r M eulen’s m ethod.

A R eply to te r M eulen an d to Schuster.

1 C ertain im provem ents m ade in ter M eulen’s m ethod.

3. Destructive deoxidation by a substance capable of uniting with the oxygen, followed by a determination of its increase in weight due to oxidation coupled with the determination of any oxygen-containing products which escaped reduction (7).

4. Destructive chlorination of the substance followed by a determination of the oxygen-containing gaseous decomposition products (20).

5. Complete catalytic oxidation of the substance in a stream of gaseous oxygen, the carbon dioxide and water formed being simultaneously determined, together with a quantitative gaso- metric determination of the “oxygen consumed.”

T he gasometric determ ination of th e oxygen consumed in th e complete combustion of an organic substance, first carried o ut by Lavoisier about 160 years ago, has recently been de­

veloped by Glockler and Roberts (14) using semi-micro technic. T he d a ta given by these investigators, who con­

fined their studies to th e analysis of benzoic acid and one hydrocarbon, show th a t the mean error of their carbon deter­

m ination was —0.12 per cent and of their hydrogen deter­

m ination + 0.41 per cent. The m ean error reported for oxygen was —0.69 per cent, despite the fact th a t th e summ a­

tion of errors m ade in th e carbon-hydrogen determ ination should m ake their oxygen values high. An analysis of their 358

September 15, 1934

results revealed th a t their gasometric determ ination of oxygen consumed was inaccurate, generally being too high, this error overcompensating the effect of the errors in the carbon-hydrogen determination. No attem pt was made to correct accurately the gas volume due to changes in tempera­

ture and pressure, and the apparent concordance of their results was largely due to fortuitous compensation of errors of considerable magnitude. The same criticism applies to the results reported by Dolch and Will (9) and Dumke (10).

A fter considering the results obtained by the above five methods, it was decided to attem pt the further development of th e fifth method. This method has the advantage th a t it sim ultaneously determines carbon, hydrogen, and oxygen.

However, considerably greater precision is necessary in both th e carbon-hydrogen determ ination and in the gasometric determ ination of oxygen consumed than has yet been re­

ported. I t should be emphasized th a t in this method the determ ination of carbon and hydrogen m ust be very precise, since errors of 1 per cent in hydrogen and carbon cause errors of 8 and 2.67 per cent, respectively, in oxygen.

For the purpose of this laboratory' it was necessary to employ a micromethod using samples weighing about 10 mg.

The present paper reports the results obtained with the micro­

m ethod applied to compounds containing carbon, hydrogen, and oxygen, with and w ithout halogens. A later report will present the results obtained in the analysis of more complex substances containing nitrogen and sulfur, and on coal.

Mi c r o d e t e r m i n a t i o n o f Ca r b o n a n d Hy d r o g e n

Pregl’s combustion apparatus was modified for this deter­

m ination as follows:

A b s o r p t i o n T u b e s . The absorption tube fillings recom­

mended by Pregl were not used in the present case because the tubes have to remain connected with each other and with the combustion tube for much longer periods than is customary in ordinary microcombustion practice. The use of absorbents for water—such as calcium chloride, dehydrite, anhydrone, etc., which depend upon hydrate formation—was avoided and instead phosphorus pentoxide deposited on pumice was used, as recom­

mended by BoStius (4). Ascarite was used for absorption of the carbon dioxide. Both of these fillings have the advantage th at one can tell at. a glance to just what extent they have been exhausted. The absorption tubes were stoppered with tight- fitting p in s d u r in g

weighing, as re c o m ­ m e n d e d b y Boetius.

a n d w ere w eighed filled with oxygen.

Co m b u s t io n Tu b e.

Pregl’s so-called Uni­

v e r s a l fillin g w'as f i r s t u se d , b u t on attempting to c a r ry out blank q u a n t i t a ­ tive oxygen transfers th r o u g h th e heated combustion tu b e , it w as fo u n d t h a t as much as 2 cc. of oxy­

gen disappeared dur­

ing each experiment.

B y a p ro c e s s of elimination, the loss of oxygen was traced to the copper oxide- lead chromate portion

of th e tu b e fillin g . F i g u r e 1.

Since th e o th e r p o r ­ tions of the Pregl filling

were found to introduce no errors in the gas transfer, they were re­

tained and it was merely necessary to replace the copper oxide-lead chromate filling with some other substance which would not cause this error. The successful use of a catalytic method in both macro- and micromethods (IS) of combustion analysis suggested its trial for the present purpose. It was found that- a 40 per cent palladium-asbestos catalyst, when used with the other reagents recommended by Pregl, gave accurate results for carbon and

359 hydrogen. To insure complete combustion, the vaporization of the sample must be conducted somewhat more carefully than usual, since in this case the oxidation mast all be done by gaseous oxygen which passes through the tube during the combustion.

Further details of this method including the results obtained and a discussion of the advantages will be presented in a separate communication from this laboratory.

P u r i f y i n g T r a i n . Commercial oxygen, 99.5 per cent pure, was taken from a high-pressure tank and stored in a Haack Universal gasometer. From here it passed successively through a Pregl pressure regulator (A, Figure 1): an electrically heated Bock-Beaucourt platinum-asbestos purifier, B, which ^oxidized impurities; a spiral cooler: a large U-tube, C, the first arm being filled with Ascarite and the second with phosphorus pentoxide on pumice; a Friederich flowmeter, D, adjusted to permit 3 to 4 cc. of oxygen to pass per minute; a small U-tube, E, filled like the large one; and thence into the combustion tube. It was necessary to replace the Pregl bubble counter by the Friede­

rich' flowmeter since the bubble counter formed a liquid seal which prohibited free diffusion of the oxygen in the closed system.

Ap p a r a t u s f o r De t e r m i n i n g Ox y g e n Co n s u m e d d u r i n g a Co m b u s t i o n

This apparatus is a combination of some of th e features contained in the work of Glockler and Roberts, Dolch and Will, and Dumke and is shown schematically in Figure 1.

The principle of the m ethod consists essentially in carrying out the combustion in a closed system of known volume and in . determ ining th e oxygen consumed and the

oxygen in the combustion products. To de­

term ine the oxygen consumed it is necessary 3 to have th e system a t known equilibrium

conditions of tem perature and pressure both

£ a t the beginning and the end of the

combus-M tion.

Sc h e m a t ic Re p r e s e n t a t i o n o f Ap p a r a t u s

Circulation of the oxygen over the sample during the com­

bustion was maintained by means of the Sprengel pump OSTP, the rate of pumping being controlled by the rate of admission of mercury through stopcock 0 from a constant-level tube, R, supplied by a‘ 100-cc. buret, Q. The oxygen from the pump is delivered to bulb T and thence through the flowmeter, combus­

tion and absorption tubes, manometers, and back to N . The combustion of the sample is thus carried out by means of this I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y

known volume of oxygen present in the system. As the oxygen is consumed during the combustion, it is displaced by mercury which collects in T. The total amount of oxygen finally con­

sumed is then determined, after temperature and pressure equilibration, by running mercury out of bulb T, through the side tube, II7, attached to stopcock P until the level reaches the scratch, X ; the mercury is then weighed. From the weight of mercury thus obtained, the volume of oxygen which it has dis­

placed can be calculated. The water and carbon dioxide formed during the combustion are absorbed in tubes H and J and from their increase in weight the oxygen content of these products can be calculated. With these data available, the oxygen in the sample can be calculated and is equal to the oxygen in the combustion products minus the oxygen consumed.

D e t e r m i n a t i o n was determined by means of pressure-volume measurements.

Previous investigators have completely neglected this fact and consequently the values they give for oxygen consumed are inaccurate.

Since microsamples were burned, it was found that to get accurate results the total volume of the system had to be kept as small as possible, so that the volume of oxygen consumed during a combustion was an appreciable fraction of the total oxygen originally present. If this precaution was not taken, one encountered the difficulty of getting precise values from small differences in relatively large numbers.

In order to get accurately determinable initial and final conditions of temperature and pressure in the apparatus, the whole apparatus was surrounded by a practically air-tight wooden box which had removable glass front and top panels, so that the apparatus was, in effect, completely isolated from the room. Two small fans were mounted inside the box, a t either end and not directly opposed, the motors being mounted outside the box so that the heat generated by them was dissipated out­

side the box. Temperatures were read to =*=0.01° C. by means of two calibrated thermometers inserted through the top of the box, one just adjacent to the Sprengel pump and the second just above the butyl phthalate manometer, L. Barometric pressure was read on a precision Paulin barometer to =*=0.1 mm. using a magnifying glass. The pressure in the apparatus was determined by means of the butyl phthalate manometer which was read to

=*=0.01 mm. of mercury. This manometer was provided with a stopcock so th at it could be closed off during pumping periods or when the apparatus was not in use, thus avoiding the possi­

bility of the manometer contents being sucked or blown out of the tube. A mercury manometer, M , also was used in the experi­

ments on the determination of the volume of the apparatus and in controlling the pressure in the apparatus during pumping, and was read to =*=0.1 mm. To avoid sticking, the mercury was

360

lubricated with a small amount of butyl phthalate; it was found that before taking a reading it was necessary to shake the ma­

nometer slightly so as to wet the tube walls with the phthalate and thus lubricate the mercury columns. Since both manometers were in line with the air currents generated by the fans, the made approximately th at present initially.

The heaters consisted of nichrome coils mounted on a circular Transite support in front of each fan, so th at when the current was on the heated air was immediately put into circulation.

The thermoreguiator (Figure 2) was made of very thin copper tubing in the form of a grid (total width 45 cm., height 32 cm., with 10 pairs of staggered uprights connecting the two horizontal feeders), and was filled with toluene. The thermoreguiator actuated the heater through a vacuum tube-operated relay, in a circuit shown in Figure 3. By means of this apparatus con­

stant temperatures more or less independent of the room tem­

perature were obtained in the box after about 30 minutes.

D e t e r m i n a t i o n o f V o l u m e o f A p p a r a t u s . The filled of the mercury in the apparatus carefully adjusted to the scratch, X , and stopcock P closcd. The oxygen from the supply gasome­ maintained approximately the same by adjusting the resistances.

At the end of 30 minutes readings were taken of the two ther­

mometers, the phthalate manometer, and the barometer, and repeated a t 40 and at 50 minutes. At the time of the last readings the position of the mercury level of the mercury ma­

nometer was taken with respect to the zero mark of the right arm.

To insure th at the changes in temperature and pressure in the apparatus had responded to the changes in the atmosphere surrounding it, pressure-temperature calculations were made for the 30-, 40-, and 50-minute readings and the calculated pressure values compared with those observed. For sufficient precision the agreement must be within 0.1 mm. Typical data and calcu­

lations are given in Table III.

When constant P-T conditions were obtained, as indicated by the agreement between the calculated and observed pressure values, the final temperature and pressure were noted and represented the equilibrium starting conditions. The starting pressure and temperatures given in Table III are 741.52 mm.

3 0-40 741.50 299.29 299.26 741.58 741.52 0 .0 6

4 0-50 741.52 299.29 299.29 741.52 741.52 0 .0 0

a P i is calculated from th e equation: p , - ô £ -' Ti

The heaters and fans were then turned off, the thermoreguiator valve was opened, and the stopcock on manometer L closed.

A N A L Y T I C A L E D I T I O N

The glass panel in front of the Sprengel pump was opened, the mercury in the leveling bulb raised until slightly above the level in the apparatus, and then stopcock P opened to permit mercury to enter bulb ?' on slowly raising the leveling bulb. This created a pressure in the entire apparatus which could be followed by its effect 011 the mercury manometer, M. When sufficient mercury had been added to give the maximum readable pressure on this manometer, stopcock P was closed, the heater and fans were again turned on, and the thermoreguiator valve was again closed when the initial temperature was approximately reached.

Establishment of equilibrium conditions was determined in the same manner as described in the preceding paragraph.

Since the increase in pressure in the closed system was caused by a decrease in the gas volume equal to the volume of m ercury added to bulb T, it was necessary only to determine this volume of mercury in order to calculate from the initial and final equilibrium pressures and temperatures the volume of th e closed system. The added mercury was run out through the side arm , W , and weighed, its volume being cal­

culated from its density a t the final tem perature prevailing in th e apparatus. The volume of the apparatus can then be calculated to the zero line of both manometers by means of the equation:

September 15, 1934 I N D U S T R I A L A N D E N G

i

_

1 PiT,

where V = volume of free space in the apparatus Pi = initial pressure in mm. of mercury Pi = final pressure in mm. of mercury Ti = initial temperature in 0 K.

J'i = final temperature in ° K.

a = volume of mercury added to system (calculated from the weight of mercury added)

b = sum of volumes added or subtracted by depression or elevation of the manometer fillings from the zero mark (1 mm. on mercury manometer = 0.00208 cc.;

1mm. on butyl phthalate manometer = 0.00199 cc.) The mean value obtained from five such determinations of the volume of the apparatus was 87.7 =*= 0.27 cc. Greater precision was n o t necessary, since use was made of this figure only for correcting th e volume of oxygen consumed because of changes of tem perature and pressure in the conditions a t the s ta rt and finish of the experiment. Also, since the small U- tube and absorption tube fillings were gradually exhausted, th e volume gradually increased and on refilling the absorp­

tion tubes or the combustion tube it was impossible to fill them so th a t no change in volume occurred.

Q u a n t i t a t i v e G a s T r a n s f e r E x p e r i m e n t s . W ith the volume of the apparatus known, a large number of blank ex­

perim ents were made to determine the quantitative nature of the gas transfer. In these experiments no sample was burned, b u t otherwise the technic was identical to th a t which was used when a sample was being analyzed. I t was found th a t in every experiment a small, fairly constant am ount of oxygen was lost, th e am ount increasing if the time of pumping was increased. The average value of this loss for twenty- five experiments was 0.166 cc. a t normal tem perature and pressure.

Experim ent showed th a t this loss was probably due to diffusion of oxygen through the rubber connections present in the apparatus, although all the glass ends a t such connec­

Experim ent showed th a t this loss was probably due to diffusion of oxygen through the rubber connections present in the apparatus, although all the glass ends a t such connec­