Ammoniated Peat Mechanism of Formation of Water-Soluble Nitrogenous Constituents L. B. HOWARD, L. A. PINCK, A N D G . E. HILBERT Fertilizer Investigations, Bureau of Chemistry and Soils, Washington, D. C.
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A PREV1OUs mu n ic a t i o n
The mechanism of formation of 75 to 90 per cent of the water-soluble constituents of ammoniated peat involves the production of ammonium salts of the carboxylic acids which upon continued heating are transformed by (1) decarboxylation to evolve carbon dioxide which in the presence O f excess ammonia is converted to Urea and (2) dehydration to form amides
__
Iw+*
tions For athe portion secondofseries the of Sameamextrac-
moniated peat taken a f t e r t h e Preliminary drying at 50" C. was reammoniated under the identical conditions for an additional 24
(2) on the nitrogenous composition of ammoniated peat it was shown that the major portion fe",~s;o~~~ Of the water-so1ub1e n i t r o g e n pulverizing operations, odorless, and contained 10.5per cent of to be found in hhe amide nitrogen; on standing it developed fraction. h large portion of this c o n s i s t e d of urea, suggesting other than urea. It is important that scarcely any odor of ammonia. that one of the primary reacthe ammonium s d t s be as completely tions involved decarboxylation, transformed as possible to avoid loss of Extractions the carbon dioxide thus liberammonia by dissociation upon storage. Both the original and the recont~~~~ b e i n g A consideration of the mechanism pretreated ammoniated peat were verted to urea. In view of resented indicates the Of inh a n d l e d in exactly the same sults of Davis, Scholl, and Miller (1) s h o w i n g t h a t the watercreasing the potential carboxylic acid manner as follows: content of the peat to a maximum. soluble fraction has considerable value as a fertilizer, it seemed Four hundred g r a m s of the dried pulverized material w e r e d e s i r a b l e to make a compreadded to 500 CC. of distilled water and allowed to stand with hensive study of the mechanism of the formation of the waterintermittent stirring for a few hours and then drawn off on a soluble nitrogenous constituents of ammoniated peat since BGchner funnel. Since only cc. of extract could be withdrawn under suction, this was replaced with 200 cc. of distilled such information would be useful in arriving a t conditions favoring the increase of this particular fract'ion. water and the extraction was repeated until eight such extracThe method of attacking the problem consisted essentially Lions had been made, giving a total volume of approximately 1500 cc. of filtrate (I-VI11 in Table I). In some cases the mixture of making a series Of cold Water extractions of a Sample of stood overnight before removing the extract. Extract IX peat which had been ammoniated for a relatively short time (approximately 200 CC.)was kept separate in order t o observe and of a sample of the same material which had been subthe trend of the extractions; subsequently five more were jected to further ammoniation for a much greater length of made and the filtrates were combined to give approximately 1000 cc. (X-XIV). The fraction of the ammoniated peat retime. These various extracts were then analyzed by the promaining after these extractions still contained an appreciable cedure developed in the earlier study, and the nitrogen was amount of soluble matter. classified as indicated in Table I. From the data so obtained, it is possible to deduce certain conclusions concerning the Analytical Procedure mechanism of amide formation. The total nitrogen was determined on 100-cc. aliquots of each of the solutions by the Kjeldahl method. The urea and Preparation of Ammoniated Peat ammonia nitrogen content of solutions I-VI11 and IX was determined on 5-cc. aliquots by Yee of this laboratory by a The material used in the first extraction was prepared by modification of the urease method (3). Since solutions IX conScholl from Capac Michigan, p a t by treatment at 180" C . tained no urea, it was obviously unnecessary to submit solufor 4 hours with an equal wag t of 29.1 per cent aqueous amtions X-XIV for urea determination, and the ammonia determonia; the pressure in the system mas 498 pounds per square mination was performed on a 100-cc. aliquot by vacuum disinch (35 kg. per sq. cm.). After a preliminary partial drying tillation at 60" c. with 1 gram of magnesium oxide and 50 co. in the autoclave at 50" c. and 150 mm. of pressure for 100 of alcohol into standard acid. The amide determinations were hours, the material nras further dried by distributing it on clay carried out in exactly the same manner as described in the preplates which were placed over sulfuric acid in desiccators and vious communication (2) using aliquots of 100 cc. The xanthysubjected to vacuum desiccation to constant weight. The dried drol modification was applied only to the solutions containing product was pulverized in a ball mill and when so obtained was urea (I-VIII). odorless and contained 7.9 per cent of nitrogen. On standing To determine the amounts of water-soluble nitrogen after for a few weeks in a stoppered container it developed a strong in 20 per cent hydrochloric acid, 5 grams each of the hydrolysis odor of ammonia. 1508
fizFjrY:ii:s
DECEMBER, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
original ammoniated peat and the retreated product was added to 100 cc. of the acid and refluxed for 96 hours. The mixtures Tere taken to dryness in vacuo to remove the hydrochloric acid, and the residues leached with water. The filtered extracts were made up to 500 cc., and 50-cc. aliquots were withdrawn for total nitrogen by Kjeldahl. The analytical results are recorded in Table I. TABLE I. COLDWATERFRACTIONATION OF AMMONIATED PEAT Extracts
I-VI11
IX
x-XIV Total
I-VI11 IX
x-XIV
Ammonium S
Urea
%
%
s
Other Amide Unclassified N N
%
Total N
%
%
Original Ammoniated Peat" 8.1 1.2 2 0 0.3 ... 0.1 1.4 ... 0.2
3.3 0.3 0.6
-
14.6 0.7 2.2
-
9.8
4.2
17.5
2.3 0.1 0.2
16.7 0.3 0.8
-
__
-
1.2 2.3 Retreated Ammoniated Peatb 3.6 3.2 7.6 0.1 0.1 0.4 ... 0.2
-
... _-
-
-
-
Total 3.7 7.6 3.9 2.6 17.8 a Contained '737' nitrogen of which 44.7% was soluble in water after g6-hour digestion $ith 20% hydrochloric acid. b Contained,lO.S% nitrogen of which 38.37' was soluble in water after 96-hour digestion with 20% hydrochloric a d .
Discussion of Results Previously the writers suggested that the formation of urea in the ammoniation of peat resulted from a decarboxylation of the peat followed by a urea synthesis from ammonia and the carbon dioxide so liberated. In order to test this hypothesis, the present investigation was carried out and the data obtained not only amply confirm the former speculations but also yield considerable information concerning the whole mechanism of amide formation. Table I shows that the total nitrogen content of peat ammoniated for 4 hours increased markedly (from 7.9 to 10.5 per cent) by continuation of the process for an additional 24 hours, while a t the same time the proportion of nitrogen which is soluble in cold water1 remained nearly constant (17.5 and 17.7 per cent). However, after hydrolysis with hydrochloric acid, 44.7 per cent of the nitrogen of the former was water soluble as compared to only 38.3 per cent of the latter. Therefore it is evident that, although the total amount of nitrogen introduced may be increased by extended heating, the purpose-namely, the preparation of a relatively watersoluble nitrogenous material-is to a certain extent defeated by the concurrent increase in insoluble nitrogen. It would appear that this augmented insoluble nitrogen is mainly in the form of complex cyclic nitrogen compounds resulting from the condensation or polymerization of products perhaps formed by the ammonolysis of oxygen compounds or by the addition of ammonia to unsaturated linkages. The presence of such complex cyclic nitrogen compounds in the insoluble nitrogenous fraction of ammoniated peat seems likely, since it accounts for the insolubility and the resistance towards hydrolysis by hydrochloric acid of the material. At any rate the formation of the above product is probably not connected with amide formation and hence was not further investigated. Significant is the relationship between ammonium, urea, and amide nitrogen, other than urea elutriated in the fractional aqueous extraction of these two specimens of ammoniated peat. For example, 9.8 per cent of the total nitrogen in the original sample was present as ammonium nitrogen in these extracts as compared to only 3.7 per cent in the correspond* Cold uater was specifically used in the extraction t o hold hydrolysis t o a minimum.
1509
ing extracts of the retreated material. This decrease in ammonium nitrogen, when the length of time of treating the peat is extended for an additional 24 hours, is accompanied by an increase of from 1.2 to 7.6 per cent of urea nitrogen and from 2.3 to 3.9 per cent of amide nitrogen. That the increase in the urea and amide nitrogen takes place a t the expense of the ammonium nitrogen is apparent. It is interesting to note that the various types of soluble nitrogenous material, except the urea, persisted, although with a gradual tapering o f f , through fourteen consecutive extractions. This emphasizes the complex nature of the ammonium salts and amides, since the simple analogs possess considerable solubility in cold water and would be expected to be removed by a few extractions. That the ammonium salts, a t least in part, are compounds of very weak acids is indicated by the gradual loss of ammonia, presumably by dissociation from the original sample upon standing even after previous thorough desiccation. For this reason the ammonium nitrogen in the original ammoniated peat is undoubtedly much higher than the recorded value observed after desiccation. From these data and considerations it may be concluded that the mechanism of amide formation involves f i s t the formation of ammonium salts of carboxylic acids. These are subsequently transformed to an extent dependent upon the temperature and duration of ammoniation by two main courses: (1)that of decarboxylation which is the more favored reaction and yields urea and (27 that of dehydration which gives substituted amides other than urea. These reactions are as follows: RCOOH
+ NH,
RCOONH,
