0
NITROGEN DERIVATIVES OF PHOSPHORUS AND SULFUR' L. F. AUDRIETH University of Illinois, Urbana, Illinois
T o PROPERLY survey recent experimental developments concerning the nitrogen derivatives of the phosphoric acids and of sulfuric acid, it is helpful to apply a concept which has already proved to be of inestimable value in systematizing the chemistry of the nitrogen derivatives of carbonic acid. No unifying concept has been of more value in the elucidation of the chemistry of the ammonia derivatives of carbonic acid than the Franklin solvent system approach, ( 1 . B ) s~ecificallvas it relates to a consideration of the
'
Presented im part of the Symposium on Recent Advances in the Chemistry of Inorganic Nitrogen Compounds before the Division of Chemical Education at the 131st Meeting of t h e American Chemical Society, Miami, April, 1957.
VOLUME 34, NO. 11, NOVEMBER, 1957
many and varied compounds that can be designated a.3 ammono and mixed aquo ammono carbonic acids (3). A consideration of water and ammonia as parent suhstances of systems of compounds makes it possible (1) to organize the chemistry of oxygen and nitrogen compounds as aquo and ammono compounds, respectively, (2) to compare the properties of such ammono compounds with the better-known oxygen compounds, and (3) to develop methods of synthesis for nitrogen compounds, entailing reactions of ammonolysis, ammonation, and deammonation, that are in many respects similar to reactions of hydrolysis, hydration, and dehydration. Rather than use a specific terminology, i t seems more reasonable to speak of such synthetic
reactions as involving solvolysis, solvation, and desolvation processes, especially since the general utility of the solvent system concept has been extended to many other parent substances such as the amines and the alcohols, to hydrazine, hydroxylamine and their N-substituted derivatives, to hydrogen sulfide and to a large number of nonprotonic solvents. The principle of analogy is a useful one, hut it cannot be applied indiscriminately. Profound differences are frequently observed. These must be recognized and considered a s inherently specific for the classes of compounds under discussion. Consideration of the nitrogen componnds of phosphorus(V) and sulfur(V1) as ammono or as mixed aquo ammono derivativeswell illustrates the three advantages just mentioned. It also becomes possible to compare the chemistry of the ammono and aquo ammono phosphorus(V) and sulfnr(V1) compounds with reactions which the ammono and aquo ammono carbonic acids, for example, urea, cyanamide, cyanic acid, melamine, cyanuric acid, and guanidine, have been found to undergo. The ammonia derivatives of carbonic acid have long been known and the chemistry of these substances has been developed in detail. Technologically, these substances have achieved importance as industrial chemicals. By contrast, the nitrogen derivatives of the phosphoric acids and of sulfuric acid are not so well known. They are, however, slo~vlyhut surely eliciting the academic interest and industrial attention which they deserve. A detailed comparison of the corresponding carbon, phosphorus, and sulfur componnds does lead to a very interesting and important conclusion, namely, that the reactions of these anlmono compounds depend to a large extent upon the attached amido- and imidogroups. Here again, care must be exercised not t o overextend such analogies. Due consideration must be given t o variations in size, charge, and relative electronegativities of the respective elements and to bond strengths of the X-N linkages in the ammono compounds of carbon(IV), phosphorus(V), and sulfur(VI). Trends are clearly recognizable. Yet to a large extent it is the chemistry of nitrogen which must he considered as of paramount importance, rather than the special properties of the respective central atoms.
-
7"- do-
NHI
>H
NHa
NH,
/ c=o\NHB
c=o
O 'H
-C=NH
\NHI
HOCN
H2NCN
I
I
4
L
(HOCN), Fiwr. 1.
/
(HINCN)~
-
Th. Aqua Ammono Csrbonic Acid.
CO(OH),
COI
-
NHI
/
C=NH
\
-
/NH2 C u HN(CN).
I
B
NH2
N
1 /
NHx
G=NH
\
(GIN,).
[HN(CN)ala
NHCN
+
(CNNHdr Figure 2.
Th* Ammono Clubon10 Acids end Thai. Da-mmon.tion (and Polym.rii*tion) Product.
2. All of the ammono and q u o ammono compounds react as acids in liquid ammonia, even though their chemicd nature with respect to water as a solvent is quite varied. These substances are therefore properly designated as ammona and squo ammono carbonic acids. 3. Many other reactions which these substances undergo me more characteristic of the attached nitrogen groups. I n presenting these type reactions it should again be emphasized that specific effect8 often alter the detailed nature of such reactions. Alternative reactions must also he considered; these sometimes occur preferentially. A few of the more common reactions are summarized in Table 1.
Reactions of Ammono Acids Ammono acids: X-NH, N-alkylation: X-NHNa Hydrolysis:
+ NHa + RX
-
+ NH,+
XNH-
-
XNHR
+ NsX
To emphasize the chemical relationships which are now being developed among the N derivatives of the PO') and S(V1) compounds, respectively, it would seem desirable to review briefly the chemistry of the better known ammono and aquo ammono carbonic acids. These are represented diagrammatically in Figures 1 and 2. The generic relationships developed on the basis of the ammonia-water analogy and depicted in Figures 1 and 2 have been verified experimentally.
H+ X-NHn H20 X-OH NHa.Ht (the X-N linkage is more stable in alkaline aqueous solution than in acidic media) Reaction with aldehydes: X-NH* CH.0 X-N(CH90H)~ or X-N=CH, Reaction with nitrous acid: X-NH2 HONO X-OH Nn H 2 0 X-NHHONO X-N(NO)H,O Deammonation: A H X-N-X NHI 2[X-NH*] N-chlorination: OCIXNC1H20 X-NH2 Acylations: H X-NH2 RCOX (RSO,X, (RO),POX, etc.) X-NCOR, etc. Polymerization: [-X=N-I, -X=N
1. Reactions leading t o the ammono compounds entail processes of ammonolysis, ammonation, or deammonstion. Thus, for instance, the action of ammonia on phosgene to give urea represents an ammonolytic process. The addition of ammonia to carbon dioxide is an ammanation reaction; the treatment of urea. with potassium hydroxide to release ammonia and form potassium cyanate can he regarded as a deemmonation reaction.
It should be emphasized that similar reactions may be expected to characte~izethe behavior of the ammono phosphoric and the ammono sulfuric acids, even though the confirmatory experimental evidence has not yet been adduced in all instances.
AMMONO AND AQUO AMMONO CARBONIC ACIDS (3)
+
-
+
++
+
+
-
--
-
-
+
+ ++
+ +
-
JOURNAL OF CHEMICAL EDUCATION
THE AQUO AMMONO AND THE AMMONO PHOSPHORIC AND POLYPHOSPHORIC ACIDS
acids. The preparation of phosphorus oxytriamide (6) and the corresponding thiono derivative, PS(NHsjZ, has been effected by the addition at low temperatures of the respective chlorides in chloroform solution to an excess of ammonia also dissolved in chloroform. Goehring (7) has improved the preparation of phosphorus oxytriamide by operating at still lower temperatures using liquid ammonia. This substance undergoes hydrolysis in aqueous sodium hydroxide to give the monosodium salt of phosphorodiamidic acid. Exposure t o a moist atmosphere results in the gradual formation of the diarnrnonium salt of phosphoramidic acid. It is possible, although methods have not yet been worked out to do so, that these hydrolytic procedures for bringing about conversion of the triamide to the corresponding mono- and diamido- derivatives of phosphoric acid may supersede the older method for the preparation of both of these substances. Stokes (8) prepared these from the corresponding phenyl phosphorochloridates. Use of liquid ammonia to effect conversion of the chloridates to the corresponding
A purely formalistic scheme may he employed to represent the relationships which obtain among the "aquo" phosphoric, polyphosphoric, and metaphosphoric acids. The preparative methods which are employed to accomplish such aggregation reactions entail dehydration (molecular condensation) reactions. The structures of such "polymeric" products, derivable from orthophosphoric acid, can best he pictured and rationalized by emphasizing the tendency for P(V) t o assume, with few exceptions, a tetrahedral configuration. The tetrahedral PO4 unit is the structural entity in all phosphates, polyphosphates, and meta~hosphates. Corresponding ammono and aquo ammono phosphates may also undergo aggregation by deammonation reactions leading to polyammonophosphates, in which the tetrahedral configuration of phosphorus(V) is retained. These relationships are depicted in Figures 3 and 4. The relationships developed in Figures 3 and 4 represent only the simplest aspects of the chemistry of these phosphorus-nitrogen comNHa pounds. Many of the N-substituted OH compounds, that is, derivatives in OF-OH/ which the hydrogens of the amide \OH or of the imide nitrogens are replaced by organic groups, are better OLPO(OH),I known. These have been discussed in exemplary fashion by Kosolapoff or (4) in his outstanding treatise on (HPO,)..H,PO, "Organo - phosphorus Compounds." or o further reference will be made t o such organo phosphorus-nitrogen (HPO&,c,, compounds in the prePent discussion except to point out that a new system of nomenclature has been proposed and is now coming into general use. Monoamidc- and diamidophosN[P&OH).I~ Figur. 3. The Aquo end Aquo Ammon. Phosphoric Acid. pholic acids are thus more correctly designated in terms of the newer nomenclature as phosphoramidic and phosphorodiamidic acids. Although the simpler compounds can be named t o conform with this system, it becomes a more difficult task to name the compounds in which a bridge oxygen atom between two phosphorus atoms is replaced by a bridge nitrogen linkage. I The chemistry of the phosphorus-nitrogen com0 0 pounds does require some thorough re-investigation and re-evaluation. Such investigations are now underway by Klement and by Goehring and their students at -0 Munich and Heidelberg, respectively. In this country, P O - ' (from HaPa01) P+012-4(horn HZ&) only a limited amount of work is underway iu academic Metaphosphates laboratories. Industrial producers and consumers of phosphate chemicals are, however, active in this field. Only the preliminary work of Quimby (5) has thus far seen the light of day in a scientific publication. Work on phosphorus-nitrogen compounds is also being carried out under the auspices of various military agencies with the objective of synthesizing and developing inorganic polymers, elastomers, resins, adhesives, lubricants, and other materials to withstand highPhosphonitrilio compounds temperature conditions. (where X = F, C1, Br, OH, OR, NH,, NHR, N R s SR, Ar, etc.) Klement has been particularly active in developing rimre 4. The Ammono Phosphoric Arid. and the Phanhonittilic Comp.und. analogies between the aquo acids and the ammono
.1
VOLUME 34, NO. 11. NOVEMBER, 1957
undergo deammonation to the more highly condensed product, imido bisphosphoric diamide, by reaction with dry HC1 in ether a t temperatures below 0' (12). At higher temperatures a greater quantity of dry hydrogen chloride is absorbed and condensation to compounds containing a higher phosphorus-nitrogen ratio is achieved. The exact compositions of these products have not yet been determined. Ammonolysis of pyrophosphoryl chloride, PIOICId, leads to the corresponding tetramide, Pz03(KHz)r(12, 19). I t is well known that the mono- and dihydrogeu orthophosphates undergo aggregation reactions a t higher temperatures with formation of poly- and metaphosphates. Klemeut (14)has shown that deammonation reactions, accompanied in some instances also by elimination of water, take plare readily when the sodium salts of phosphoramidic and phosphorodiamidic acids are decomposed thermally. The disodium salt of phosphoramidir acid undergoes deammonation to give the tetrasodium salt of imidodiphosphoric acid. This particular compound forms a 10hydrate wheu recrystallized from aqueous solution and a tetrasilver salt which resembles the pyrophosphate. The free acid is presumably obtained in solution by use of a cation exchanger. Sodium phosphorodiamidate reacts with silver ion to give a pentasilver salt which must have the structure represented by the formula AgOPO(KAg,), (15). The latter reacts with methyl iodide to give a product whose composition can be represented by the formula, Ag01'O[N(CH3)2]2; dimethylamine is obtainable on hydrolysis. The sodium salt, vhen heated a t 155" for some time, loses ammonia and is converted int,o a polymeric product which can be represented by the composition XaaPz06(KH)2(NH2)~. Only the amido groups react with nitrite in the prePerice of perchloric acid, leaving the bridge imido groups intact. Such
phenylphosphoroamidates does have advantages over the use of aqueous ammonia or reaction with gaseous ammonia in some nonaqueous solvent (9). The amidates are but slightly soluble in liquid ammonia, whereas ammonium chloride is quite soluble. The phenoxy groups are subsequently removed by the actiou of concentrated alkali. The greater stability of the PN linkage in alkaline solutions is to be noted. The free acids can be prepared from the salts by ion exchange (10). The synthetic methods may be depicted diagrammatically as follows:
CsH,0PO(KHz)2
NaOPO(NHJ2
(CeH,O)zPONH,
Na2POaNH3
Thermal deammonation of 1'O(KH2)3 leads to a
substance which is undoubtedly polymeric in character and which might be called a phosphorus (V) oxy-imideamide. This same substance has presumably also been obtained by Goehring (11) by the action of POCl3 upon a suspension of phosphorus oxytriamide in ether, followed by treatment of the intermediate product with liquid ammonia to effect complete ammonolysis and removal of ammonium chloride. Goehring presents an 8-membered ring structure for the resulting product in which the phosphorus atoms are linked together by imide groups. Complete deammonation of either phosphorus oxytriamide or of the imide amide leads to a highly polymeric substance, (POX),, whose structure has not yet been established. The phosphorus(V) oxynitride is so stable that fusion with alkali is necessary in order to bring about its decomposition. The phosphorus(V) oxytriamide can he made to
TABLE 2
-
Reactions of the Ammono Phosphates
POCI.
PO(NH&; PSCls PS(NH& liq. NHI heat heat [PO(NH)(NHJl, ---+ (PON),
,-
I
1
1 NaNO*, HClO, L-----
PO(SHr):, POCla H a
-1
-11
-
NHa-CHC4
NsOH
HCI U N ether,
product
NH,
[NePO2NH1, (insol.)
[PO(NH)(NH?)l&
(NH&PO,NH, h.rtPO3(NH2), H [P0(NH?),JX
-15'
liq. NH:, PIOSCI,--A P10dNHd4 NH,-CHCII Me1 Ag yAgOPO(NAg?), AgOPO(NMe& 0 0 0 NePOS(NH& 155' NaNO? Ag+ -- NH?-P-NH-P-NH-1'-NH. ---4 - AglP308(NH)1 0 0 0 HCIO, Nn Na Ns 230" (vac.) L [Ns;P02(NH)],, heat Ag+ +Ag4P20sNH Na?POaNH. -----t (Na0)2PO-NH-P0(0Ns). +
548
JOURNAL O F CHEMICAL EDUCATION
treatment gives a product from which an insoluble silver salt corresponding to the formula Ag5P,08(KH)2 can be obtained. This would correspond to a di-imido triphosphoric acid derivative. At still higher temperatures and after long heating in vacuum at 2.70°, the sodium phosphorodiamidate undergoes further deammonation to give a product whose composition ran be represented by the formula [NaP02(NH)],. This is certainly a sodium ammono metaphosphate. It dissolves slowly in water to give a viscous solution. A product of the same composition, obtained by action of nitrous acid on phosphorus(V) oxy imide amide, is insoluble in water and presumably even more highly polymerir. In all of this work with the ammono phosphates and ammono poly- and metaphosphates, existence of higher molecular weight polyanionir species seems to have been fairly well established by employment of both chromatographic procedures and ion exchange methods. Indeed, if these two experimental procedures had not been used, a question might still be raised concerning the nature of the very unusual products obtained as a result of both hydrolytic cleavage of pbosphorusnitrogen compounds and their high-temperature deammonation reactions. Some of the more important chemical reartions described above, dealing with t,he ammono phosphoric arids, are summarized in Table 2. THE PHOSPHONITRILIC COMPOUNDS
(16)
The phosphonitrilic halides and their derivatives represent one of the most unusual classes of inorganic compounds that have ever been isolated. Preparation of the phosphonitrilic chlorides entails the partial ammonolysis of phosphorus pentachloride by ammonium chloride, either in an appropriate solvent or by direct interaction at temperatures above 130". Symmetrical tetrachlorethane has usually been employed, although other solvents like orthodichlorohenzene may also be used. Complete ammonolysis of phosphon~spentachloride leads to the phosphonitrilamides. The phosphonitrilic bromides have been made by a similar reaction between phosphorus pentabromide and ammonium bromide. I t is only recently that the preparation of the phosphonitrilic fluorides has been effected by interaction of the chlorides with potassium fluosulfinate a t 125°C. (17). The partial ammonolysis of the pentachloride (or pentabromide) leads to a series of polyhomologous compounds with the empirical formula PNX2. The reaction product consists of two crystalline polyhomologs, the trimer and the tetramer, and a mixture of higher polyhomologs for which the value x in (PNXz), varies from 5-7. Reference will be made later to the structures of these substances. I n view of the fact that the attached chlorine (or bromine) atoms in the phosphonitrilic structures are still quite reactive it is possible t o further effect either partial or complete solvolysis. The action of water, ammonia, arnines, and alcohols leads usually to partially solvolyzed phosphonitrilic derivatives,suchas P2N8Cl& where X = OH, NH*, NHR, NR2 or OR. With some amines completely solvolyzed N-substituted derivatives can he obtained. In some instances, use of an alkali metal derivative of the solvolytic agent can quickly effect the complete replacement of the VOLUME 34, NO. 11, NOVEMBER, 1957
active halogens, as for instance, when the PNC12 trimer and the sodium alcoholates react in the respertive alcohol as the solvent (18). The phosphonitrilic halides can also be subjected to action of Grignard reagents, in which the active halogens are partially or completely replaced by aromatic groups. In the presence of aluminum chloride it is possible also to carry out a Friedel-Craft type reaction which apparently goes no further than to for111 a diphenyl or ditolyl derivative in the case of the trimer (19,20). The situation is quite interesting in the case of the tetrameric form of PKC12. Here the action of Grignard reagent results in the replacement of four or eight of the chlorine atoms of the tetramer. Two isomers of the compound in which only four of the chlorine atoms have been replaced have been prepared (21). It is also claimed that t ~ isomeric o forms of the completely phenylated derivative have been synthesized although no satisfactory explanation for the observed differences has been presented. It is conceivable that these correspond t o a chair and a boat form of the tetramer. The chlorine atoms on t.he phosphonitrilic chlorides are replaced in pair-wise fashion. This has been substantiated by subjecting either incompletely or completely phenylated derivatives to hydrolysis; diphenylphosphinic acid is obtained ($0). Careful hydrolysis of both the trimer and the tetramer leads to the metaphosphimic acids, in whirh the ring structures are retained. These phosphonitrilic acids are, however, quite unstable and susceptible to further hydrolytic or solvolytic cleavage. Stokes, who first investigated these con~pounds,claimed that hydrolytic cleavage of these ring structures resulted in the formation of polyammono phosphoric acids in which the phosphorus atoms were connected through imido bridges. Quimby and ro-workers (5) have more recently studied this whole phenomenon and, on the basis of chromatographic studies of such hydrolysis products, have come to the conclusion that the principal reactions entail stepwise replacement of nitrogen atoms in the cyclic phosphonitrilic derivatives by oxygen. This process undoubtedly involves hydration and ring opening followed by ring closure with the elimination of ammonia. That the nitrogen atoms of the phosphonitrilic compounds still possess definitely basic character would seem to be evidenced by the fact that the trimer of PNCL is capable of adding three molecules of sulfur trioxide in what might be looked upon as a typical Lewis acid-hase reaction (B). The trimer is soluble in glacial acetic arid and will react with perchloric acid to precipitate an acetic acid insoluble perchloratc salt, with the formula P3NaC16.HC10a (25). It was Stokes (24),working at Johns Hopkins University just before the turn of the century, who discovered that the products which he obtained by the interaction of PC& and ammonium chloride are capable of undergoing polymerization. He found that the trimer and the tetramer, as well as the oily polyhomologs, could, by heating to temperatures above 300°,be converted into a rubber-like material which he called "the inorganic rubber." Many investigations have been carried out since that time to study further this amazing polymerization process. The "inorganic
rubber" has all of the physical characteristics of ordinary rubber. Unfortunately, it also has some of the physical characteristics of plastic sulfur, since like the latter it reverts on standing to the more stable crystalline trimer and tetramer as well as the lower oily polyhomologs. It is for this reason that the conditions leading to the polymerization of the phosphonitrilic halides and of their solvolytic products have been subjected to intensive investigation, especially since our last review on this subject was published in 1942 (16). In an effort to stabilize such polymeric substances against reversion and hydrolysis, attempts have been made to replace by solvolytic action the active chlorine atoms in the polymerized product, but all surh efforts have thus far proved to be of no avail. Attempts have also been made to polymerize the completely solvolyzed products, but the polymerization products thus far obtained do not possess elastomeric characteristics. Polymerization of partially phenylated and solvolyzed products can also be made to take place, but again, the resulting products do not possess the desired characteristics of the polymers obtained from the phosphonitrilic fluorides, chlorides, and bromides. The structures of the trimer and tetramer have been fairly well established and have been shown by both physical and chemical structure studies to consist of 6- and 8-membered phosphorus-nitrogen rings, respectively. There is no question but that these 6- and 8membered rings can be represented by a number of resonance structures and that the PN linkage possesses partial double-bond character. The trimeric phosphonitrilic ring is therefore benzene-like in behavior, as evidenced by the fact that such substances can undergo typical Friedel-Craft reactions (SO), and also reaction with Grignard reagents. Less well defined are the structures of the lower polyhomologs, with a degree of polymerization represented by 5 to 7 PNX2 units. These polymerize much more readily. There is a sharp change in physical properties in going from the crystalline trimer and tetramer to these higher polyhomologs. We had suggested (16) that these higher polyhomologs could be depicted as chain structures, but recognized that such a suggestion is perhaps not too tenable. Such chain structures would represent unsaturated, perhaps radical-type, compounds. It has been proposed more recently that the higher polyhomologs are condensed trimeric or tetrameric rings ($5), but it is difficult to depict such structures or to reconcile the more ready polymerizability of the higher polyhomologs uith condensed ring structures. In 1942 (16) we proposed that polymerization of the trimer and tetramer entailed initial opening up of the ring and that the subsequent thermal aggregation reaction could be looked upon as a typical vinyl polymerization. This concept seems to have been suhstantiated more recently by German workers who have undertaken to study both bulk and homogeneous polymerization of the trimer and the tetramer (86). In has been found that oxygen is absolutely necessary in order to effect polymerization. This suggests that the oxygen serves as the initiator in activating the PNC1, molecules to bring about initial ring rupture and that polymerization then proceeds to give high molecular weight products through a radical mechanism.
SULFUR-NITROGEN COMPOUNDS
(27)
Some years ago we showed (87) that the interrelationships between sulfuric acid and compounds like sulfamic acid and sulfamide and their deammonation products could he represented by a scheme very similar to that proposed by Franklin for the ammono and mixed aqua ammono carbonic acids. Considerable interest has been manifested since that time in developing further the chemistry of the mixed aquo ammono sulfuric acids. Sulfamic acid and its derivatives have achieved considerable technical importance. The free acid and some of its salts are produced in substantial quantities. Sulfamic acid is a nonhydroscopic crystalline solid which dissolves in water to give a strongly acid solution. Its use as a primary acidimetric standard has found fairly wide application. Sulfamic acid and the sulfamate ion have been found to undergo practically all of the reactions which are listed in Table 2 as characteristic of compounds containing an attached amido group. It is a dibasic acid in liquid ammonia; it undergoes N-alkylation in liquid ammonia; it reacts with nitrous and nitric acids to give nitrogen and nitrous oxide, respectively, but at different tem-
SO,(OH)
7"
YES
- so, - SOt -\
I
[SOzNHI
NHI
Fig",..
5.
I
The Aquo Ammono Svlfu~icAcid.
peratures, thus permitting differentiation between these two anions, both qualitatively and quantitatively; N-chlorination yields an N-chlorosulfamate; deammonation of some of its salts leads to imidodisulfates. N-substituted organic derivatives of both sulfamic acid and of sulfamide are easily prepared. Of current interest is the fact that the sweetening agent known as Sucaryl is an N-cyclohexyl sulfamate (88). Additional studies have been carried out t o characterize more definitely the reaction between SO8 and ammonia under various circumstances. Sulfur trioxide and ammonia react in the vapor state to give largely the ammonium salts of imidodisulfuric acid and nitridotrisulfuric acid. Some sulfamate is also formed. The quantity of sulfamate is increased if sulfur trioxide adducts uith various ethers and tertiary amines are allowed to react with ammonia at lower temperatures. The sulfonating action of SOa is reduced hy coordination. I t had originally been shown by Sisler and Audrietb ($0) and verified more recently by Appel (SO)that the ratio of ammonium sulfamate to imidodisulfate formed when such adducts react with liquid ammonia is a function of the basicity of the electron pair donor, that is, decreases in the order: trimethylanline > pyridine > dioxane > sulfur (in the disulfur trioxide polymer, (S103)=). Among the indicated substances, the largest quantity of sulfamate per mole of SOs is obtained from the trimethylamhe and pyridine adducts, whereas only negligible quantities are obtained when the compound (SzOa)=(31) is subjected to the action of liquid ammonia. JOURNAL OF CHEMICAL EDUCATION
with liquid ammonia at low temperatures. This particular reaction has been studied in detail by Goehring (35), and has been shown to yield two primary products, namely, sulfamide and imidodisulfamide. The latter can be subjected to hydrolysis to give additional quantities of sulfamide plus sulfamic acid. According to Goehring, no higher polysulfamides are obtained as claimed by Ephraim and Michel (36). A mechanism has been formulated for this reaction based on the assumption that sulfuryl chloride ionizes to a limited extent to give the positively charged S02C1+ ion; the latter, with an electronic configuration much like that of monomeric sulfur trioxide, adds the amide ion to give an intermediate which undergoes dehydrohalogenation to form a product that can be represented by the formula, HOSON, or as monomeric sulfimide, SOrNH. I n the presence of excess ammonia the monomer ammoniates to sulfamide. Alternatively, this reaction can be looked upon as a typical nucleophylic displacement reaction proceeding stepwise through sulfamyl chloride to sulfimide and then sulfamide. Recent work by Kirsanov (37) has shown that the product obtained by Ephraim (38) many years ago from sulfamic acid and P a 6 is a trichIorophosphazosulfonyl chloride, CIaP=NS02C1, m.p. 2 3 O . The initial reaction product undergoes decomposition with loss of POC13 a t temperatures over 118°C. to give the trimer of sulfanuric chloride, (NSOC1)3. An alternative procedure for preparing this same material has been developed by Goehring and her co-workers (35), entailing the reaction of a 2 to 1 molar mixture of sulfuryl chloride and thionyl chloride in petroleum ether with ammonia. The two acid halides are always present in excess; the reaction is carried out a t very low temperatures. Sulfanuric chloride is obtained
In view of the fact that sulfamic acid and its salts under no conditions have been found to add on sulfur trioxide to give the imidodisulfate, it is assumed that the principal reaction involves addition of SO3 to the amide ion in those instances where the imidodisulfate is formed, even though the concentration of amide ion in liquid ammonia under these circumstances is very, very small (SO). This suggestion still leaves in doubt the mechanism of the gas phase reaction between SOJ and ammonia. If the reaction between SO3 and ammonia is carried out in nitromethane as a solvent. there is obtained a precipitate of ammonium trisulfate. The resulting solution contains both trimeric and tetrameric suliimide (53). Here it must be assumed that a condensation reaction has occurred, leading to monomeric sulfimide which then polymerizes to give the trimer and tetramer, together with variable quantities of a sulfonated chain product that can be represented by the formula H03S-(NHS02)sOH. Separation of the 6- and %membered sulfimide ring compounds is accomplished by utilizing differences in the solubilities of the corresponding silver salts. These can be alkylated to give the N-substituted derivatives, whose molecuIar weights correspond to the indicated states of polymerization. Sulfamide, the urea analog in the sulfur(V1) series, also undergoes many of the reactions listed in Table 2. Deammonation results in the formation of imidodisulfamide (33) and of trimeric sulfimide (34). Although it has been claimed that sulfamide can be made by the direct interaction of sulfur trioxide and ammonia at higher temperatures, efforts to repeat this work have not been successful. The usual preparative method entails the reaction of sulfuryl chloride, diluted with petroleum ether or some other inert solvent,
TABLE 3 Reactions of the Aouo Ammono Sulfuric Acids gas phase
+ NHa I CHaNOl N(SOaNHJs, HN(SO1NHd1 r--+
SO3
SO,Cl,
liq.
NHI
0'=
SO,(NH&
+ NH(SO,NH& 1 H.O+ L
1
L
d
SOCI+
S.O.C$
VOLUME
34, NO. 11,
NOVEMBER, 1957
+
+
(NH4)?SaOIo ( S O I N H ) ~ , ~ HS08(S02NH),0H
L -
+ CI-
SO1(NH&
-
+ NHISOiH
[HOSON]
NHa
SOS(P~H*)~
S.06(NH2)..2NH$ (di- Ag, Be, Hg salts) 551
2
IK=~-N IS
I
I
@-~=NI Trisulfimide
3
Trimerie SO.
I
I
SI
I
&N\
3 HN-S-NH I I S S
I
IS
CI-S
I
-CI
I
HN-S -NH
CI
?
I
NH
Tetrasulfimide
Sulfanuric chloride
Figure 6. Structvral Formules of Some Cyclic Derivatives of the Aquo Ammono Sulfuric Acids (Compared with Trimerio Sulfur Triolid.)
from the product mixture directly in this process. The r e a h o n mechanism presumably entails the intermediate formation of sulfimide and its chlorination by thionyl chloride. Sulfanuric chloride is an extraordinarily interesting substance. I t sublimes quite readily and has a melting point of about 144°C. Depending upon conditions, hydrolysis gives the expected products, namely, sulfamide, imidodisulfamide and sulfate. The close similarity between urea and sulfamide becomes evident in many of the reactions which the latter undergoes. Condensation with formaldehyde yields methyl01 derivatives, which are capable of polymerization in much the same way that the ureaformaldehyde resins have been produced. An interesting side product is a rompound known as tetramethylene disulfonitramine (39)which is presumed to have a st.ructure very murh like that of hexamethylenetetramine. This substance is extraordinarily toxic and has found some use as a rodenticide. An amide of disulfnric acid, S20L(NH2)2,has been prepared by treatment of the chloride with ammonia
Figure 7. Totrlsulfur Tetranitride and Re1.t.d Compounds. !I) Tetrasulfur tetranitride; (11) tetrasnlftir tetrirnide: (111) trithiasyl trichloridei ( I V ) suliur; (V) heptasulfarimide.
This substance has long been known. Its formation can be accomplished by the action of ammonia upon the various chlorides of sulfur and by the interaction of sulfur and liquid ammonia. No one has yet developed a satisfactory mechanism to account for either one of these very unusual reactions. The monomeric form of N4Sl is unknown. One might theoretically compare such a monomer with nitric oxide, yet a profound difference arises immediately from a consideration of the relative electronegativities of the constituents in thionitrosyl and in nitric oxide. Nitrogen is the more electronegative component in the sulfur compound. The unknown monomeric form could he represented by a number of the resonance forms (see Figure 8). Nitric oxide exhibits a tendency to lose electrons to form the positively charged nitrosyl
740).
Some of the reactions which have been discussed above and which have represented the extensions of the chemistry of the aquo ammono sulfuric arids since the publication of our review some years ago are presented in Table 3.
(C)
-
(D)
Polymerization of BN, (SN), or &N4 Mechanism: (1) coordination (D); (2) ionic (C); (3) radical 1,4srldition.
TETRASULFUR TETRANITRIDE AND RELATED SULFUR-NITROGEN COMPOUNDS (41)
I n both the phosphorus(V) and sulfur(V1) compounds, the important structural unit among the aquo and the ammono compounds, is a tetrahedral building block. Such a unit does not, however, characterize the structures of one of the most unusual groups of substances which include tetrasulfur tetranitride and elemental rhombic sulfur. The structural relationships between N&, depicted as an Bmembered ring containing alternate sulfur and nitrogen atoms, and tetrasulfur tetrimide, heptasulfimide and elemental sulfur are given in Figure 7. The trithiazyl compounds depicted as &membered rings with alternate sulfur and nitrogen atoms are also included 111 this discussion. The work of Mewsen and Goehring and their students has done a great deal t o advance our knowledge concerning the chemistry of tetrasulfur tetranitride.
Figure 8.
Totrssulfu~Tetranitrid..
6N4
ion, which is isosterir with elemental nitrogen and the cyamde gronp. Nitric oxide does not readily suffer electron reduction to form an N O species, although this point has not yet been clarified completely in view of the reaction between elemental sodium and nitric oxide in liquid ammonia. Dimerization of nitric oxide occurs with formation of a nitrogennitrogen linkage. It is this partirular species which is then capable of 2-electron addition, perhaps a JOURNAL OF CHEMICAL EDUCATION
molecule would appear to resemble reactions which butadiene undergoes. Polymerization of butadiene is believed to involve either an ionic or a radical type mechanism and may entail either 1-2 or 1 4 addition. If polymerization entails essentially activation of the dimer by, let us say, molecular oxygen or by some other radical initiator, the mechanism proposed by Goehring for disulfur dinitride seems plausible, even though the experimental evidence has not yet been adduced. Dimerization of sulfur nitride mould appear to entail a 1 4 addition on the part of two activated N2S2molecules. The activated form can be considered as a radical former mith a shift in the double bonds from 1,3 posit,ions to the 2 position. Consideration of this mechanism leads to justification of the assumptions that Goehring and her co-workers have made with respect to the average oxidation number of 3 for sulfur as determined chemically. An ionic or a coordination polymerization mechanism can also be postulated. Mesomeric shifts and resonance structures must be assumed since the sulfur-nitrogen bond linkages are the same throughout the molecule. (1.62 A,; ralculated for N S , 1.74 A.; for K=S, 1.51A,). There is no question but that the chlorination of N4Sl to give the trithiazyl chloride must proceed by way of a thionitrosyl radical. However, S4Nl can be reformed by the interaction of the tetrimide, S4X4H4, with trithiazyl trichloride in pyridine (43). Certainly there is plenty of evidence, therefore, from these rather unusual reactions, that the mechanisms whereby these processes take place involve moncmeric units, whether these he SNC1, SNH, or SN groups. Tet,rasulfur tetranitride can be reduced to the corresponding tetrimide by the action of stannous chloride in benzene. It is interesting to point out that N& is soluble in ammonia and yields, on evaporation of the liquid ammonia solution, an ammoniate, S1N2.NH3 (44, which is identical mith the ammoniate obtained by Ruff many years ago from a solution of NISa in liquid ammonia. Careful deammonation at room temperature in high vacuum leads to the dimer of thionitrosyl. Most unusual are the react,ions of the ammoniated product, S2N1.NHa, with various metallic ions in liquid ammonia (45). Thus, for instance, with lead ion the corresponding lead(I1) salt for sulfimide is obtained, but with mercuric ion a product with t,he
1,4-electron addition reaction, to produce the electronically saturated hyponitrite ion. Because of the greater electronegativity of nitrogen in the hypothetical NS monomer, there would appear to be a greater tendency to form a negative group by electron addition, than the positively charged species. There is some evidence, however, that a positive SEN species does exist as an intermediate, especially since trithiazyl chloride, (NSCl)s, is obtained by the direct chlorination of N81. If N,S4 is heated carefully in the vapor state and the reaction products chilled immediately, there is obtained the dimer, NsS2 (42). This substance, when allowed to stand in a varuum, slowly goes over to a bronze colored compound which is insoluble in all ordinary solvents and which presumably can he represented as a high polymer of sulfur nitride, (NS),. I n the presenre of moisture or alkali, N& tends to stabilize itself by formaticn largely of the tetramer, tetrasulfur tetranit,ride. Speculation and consideration of the pec~liarit~ies of the various thiazyl compounds have led us to attempt explanation of the observed phenomena in terms of the structures of the monomer, as well as the cyclic and polymeric forms. Reference has already been made to the fact that nitrogen is the more electronegative constituent with respect to sulfur in these compounds. Consequently, certain ditferences may be expected between NO and a hypothetical NS. The structure of monomeric thionitrosyl can be represented by a typical 3-electron bond configuration, as in the case of nitric oxide. Symmetry can be achieved by loss of an electron to give a positive thiazyl speries, such as undoubtedly exists in the trithiazyl compounds, or by electron addition to give a negatively charged species. The hypothetical monomer itself can he represented by two radical structures, ( A ) and (B). (See Figure 8.) If such radicals are assumed to be capable of existence, then neither a nitrogen-nitrogen nor a solfur-sulfur bond is formed. The aggregation process entails a head-to-tail polymerization and leads to the structures given in Figure 8 for the dimer, the tetramer, and the chain polymer of sulfur nitride. The dimrric confieuration with its "diene" structure ---. reminds one immediately of butadiene. The tendency for the dimer to cyclize to the tetramer or to a chain ~
~~
-
S4N4t--- S I
1
liq. &HI
+ liq. NH,
4
(SVI,
SNH, S(NH), P
in liq. NH:, I Ph++
Figure e.
VOLUME 34, NO. 11, NOVEMBER, 1957
Some Reections of Totra."lf".
Tetzsnitride
composition HgN:S is obtained. This suggests that N2S2 could he looked upon as a mixed anammonide of both ammono sulfurous and ammono sulfoxylic acids. Even though these reactions occur in liquid ammonia, it seems t o have been fairly well established that the product N& is the source of both of these ammono acids and that NzSz is not a mixture of the two. If trithiazyl chloride is subjected to ammonolysis in liquid ammonia, presumably to give the corresponding amide, [SN(NHz)l8,the resulting solution then reacts with mercuric ion to give the compound with the composition HgNzS (46). It does not yet seem to have been established whether ammonolysis leads to a trithiazyl triamide or its monomer. It should be pointed out here that there is a distinct relationship and perhaps analogy between these divalent and tetravalent sulfur-nitrogen componnds and the corresponding divalent and tetravalent carbonnitrogen compounds. The compound HNS is a nitrogen analog of sulfur monoxide, just as HNC can be considered the imide of carbon monoxide. Even though the sulfur(1V) compound is usually represented as a sulfur(1V) diimide, it is entirely conreivable that it could be better represented as the cyanamide analog of the sulfur systems and therefore he written as HzNSN. Whether such a thiazyl amide is a monomer and/or a trirner might again be considered from this point of view since the ammonolysis of cyanuric chloride leads to melamine without reversion to a monomeric structure. The probable analogy Eetween an S=N and the C=N groups in the monomeric thiazyl and cyanogen compounds would appear worthy of consideration. Such monomeric radicals are stable among the carbon compounds; they are apparently not stable among the phosphonitrilic, P=N, or thiazyl S=N, compounds. Methods of preparation and reactions suggest a more highly polymeric structure for the cyanamide analog in the sulfur-nitrogen series. Further study of this whole group of substances has led to the preparation of the so-called thionitrosylates (47). The reaction of disulfur dinitride in liquid ammonia with metallic ions of lower oxidation state leads, by a mechanism which has not yet heen determined, to the formation of thionitrosylates of the elements in a higher valence state. Thus, thallium(1) is converted to a thallium(II1) derivative, TI(NS)3; silver ions to Ag(NS)2; copper(1) to Cu(NSj2. The simple univalent salts of both copper and silver are obtained by the interaction of the tetrimide, S4NIH4, with the respective metallic ions. That these compounds contain a metal-nitrogen linkage has been verified by reaction of the silver salt with ethyl iodide and the formation of the corresponding alkyl compound, (C2H6NS)&. However, other thionitrosylates are made by a variety of reactions, such as the displacement of carbon monoxide in the dicohalt octacarbonyl, by S4N4 in benzene solution, or the formation of the corresponding compound, Ni(NS)4, by the same reaction. The cobalt derivative is paramagnetic, whereas the nickel compound is diamagnetic. After much speculation it has now been shown that the structures actually entail coordination of NzSz units. Both the dimer of thionitrosyl and its ammoniate react with the carbonyls to give the same compounds.
One of the byproducts of the reaction between the sulfur chlorides and ammonia, where the reaction is carried out by the addition of ammonia to an excess of sulfur chlorides, is a most unusual compound known as heptasulfurimide, S7NH. Tetrasulfur tetranitride, sulfur and ammonium chloride are obtained in more substantial quantities. Heptasulfurimide has properties which are almost identical with those of sulfur. I t melts a t 113'; if heated for a longer time above its melting point some ammcnia is lost and a deep red melt is formed. Its structure has been compared with that of both the tetrimide and sulfur. I t certainly resembles sulfur in its solubility behaviors. I t is not wet or dissolved by water and it is soluble in many organic solvents, such as benzene, xylene, and carbon tetrachloride. It can be recrystallized from acetone by cooling the saturated solution to -80'. I n its absorption spectrum it resembles both sulfur and the tetrimide. The area of absorption is shifted to shorter wave lengths. What is most unusual, however, is that heptasulfurimide contains an active hydrogen in the imide group which makes t,he parent compound susceptible to acetylation, benzoylation, formylation, and even sulfonation. (48,49,50) LITERATURE CITED (1) FRANKLIN, E. C., "The Nitrogen System of Compounds," (2) (3) (4) (5) (6) (7)
A.C.S. Monograph, Iteinhold Publishing Corp., New York. 1935. AUDRIETH, L. F., AND J. KLEINBERG, "Non-Aqueous Solvents," John Wiley & Sons, Ine., New York, 1953. Reference ( I ) , Chaps. X and XI. KOSOLAPOFP, G. M., "Organa-phosphorus Compounds," John Wiley & Sons, Ine., New York, 1950. NARAIH,A., F. H. LOHMAN, AND 0. T. QUIMBY, J . Am. Chem. Soc., 78,4493 (1056). KLEMENT, R., AUD 0. KOCH,Chem. Ber., 87,333 (1954). GOEHRING, M., AND K. NIEDENZU, Chem. Ber., 89, 1768 ilO.5R). ~ - ~
-
~
,
~
( 8 ) STOKES,H. N., Am. Chem. J . , 15, 198 (1893); 16, 123 (1x94) , - - .,.
(9) AUDRIKTH, L. F., AND A. D. F. TOY,J. Am. Chem. Soe., 63, 2117 (1941). (10) KL-ENT, R., Z . anorg. allgem. Chem., 260, 18 (1949). (11) G~EHRING, M., AND K. NIEDENZU, Chem. Ber., 89, 1774 (1936). (12) bid., 86, 1771 (1956). (13) KLEMFNT, R., AND L. BENEK,Z. a m r g . allgem. Chem., 287, 12 1 1 g A f i I ~ -\----
KLEMENT, IR.,
AND
G. BIBERACHER, Z . anorg. allyem. Chern.,
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(23) (24) (25) (26) (27) (28)
KLEMENT, R., "IUPAC Inorganic Colloquium at Miinster," Seot.. 1954: Verlag Chemir. GmbH. Weinstein. Y. Chem. Revs., 32, 99 (1943). SEEL,F., AXD 3. LANGER, A R ~ u )Chem., . 68, 461 (1956). DrsnoN, B. R., J . Am. Chem. Soc., 71,2251 (1949). B o m , H., Angew. Chem., A60, 67 (1938). BODE,H., AND H. BACH,Ber., 75B, 215 (1942). BODI:,H., AND R. THAMER, Be?., 76B. 121 (1943). GOEHRING,M., H. HOHENSCHUTZ, AND R. APPEL,Z. Naturforsehuno. .. 9b.. 678 (1954). BODE,H., K. B ~ ~ T O AND W G. LIENAU, Ber., 81,547 (1948). STonE.5, H.N., Am. Chem. J., 19, 782 (1897). KRAUSE, H. J., Z. Elekt~ochem.,59, 1M)4 (1955). PATAT.F.. AND F. KOLLINSKY. Makmol. Chem.. 6. 292 (1951): bee also PATAT. ~onbtsh.. . F..,AND K. FR~MBLING. 86, 718 (1955). AUDRIETH, L. F., M. SYEDA,H. H. SISLER,A N D M. J. BUTLER,Chem. Revs., 26, 49 (1940). AUDRIETH,L. F., AND M. SVEDA.,J. Org. Chem., 9 , 89 (1944); see also U. S. Patent 2,275,125 (to E. I. du Poot de Nemours and Co.), March 3, 1942.
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(29) SISLER,H. H., AND L. F. AUDRIETH, J. Am. Chem. Soe., 61, 3392 (1939). (30) APPEI.,R., A N D W. HUBER, Z. m w g . a l l g a . chem., 275, 21 (1954); Chem. Ber., 89, 386 (1956). Z. anorg. allgem. Chem., 265, (31) APPEL,R., A N D M. GOEHRING,
M., Quart. Revs., 10,437(1956). (41) GOEARING, M., A N D D. VOIGT,Z. anorg. allgem. C h a . , 285. (42: GOEHRINQ, 181 (1956). M.,A N D H. MALZ,Z. Natwfomchung, 9b, 567 (43) GOEHRING, (1954). Z.ano~g.allgem. Chem., 275, (44) BERG,W., AND M. GOEHRING, 18 (1954). M., A N D J . EBERT,Z. Nalu~forsehung,lob,241 (45) GOEHRING, ll9.55\ BERG,W., M. GOEHRING, A N D H. MALZ,Z. anorg. allgm. Chem., 283, 13 (1956). GOEHRING, M., A N D CO-WORKERS, Z. anorg. allgem. Chem., 273, 319 (1953); 278, 1, 261 (1955); 282, 6, 83 (1955); 287, 4 (1956). GOEHRING, M., H.HERB,A N D Mr. KOCH,Z. anorg. allgem. Chem.. 264. 10 (1951 ). . . (49) GOEHRI~VG, M., A N D IT. Koca, Z. Naturjorsehung, 7b, 634 (1952). (50) GOFHRING, M., AND H. HOHESSCHUTZ, N a t u w . , 40, 291 (1953).
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PEL, R. A N D M. GOEHRING, Z.anow. allgem. Chem., 271, .2(1953). A. V.. AND J. M. SOLOTOV. J . Gen. Chem. 1r.S. . . RSANOV. s.R., 20; 1790 (1950). (34) HEINZE,G., AKD A. MEUWSEN, Z. anorg. allgem. Chem., 275, 52 -- (1R.541
