Liquid ammonia as a solvent and the ammonia system of compounds

LIQUID AMMONIA AS A SOLVENT AND THE AMMONIA SYSTEM OF COMPOUNDS. VI. ORGANIC AMMONIA COMPOUNDS. PART 11. THE NITROGEN ANALOGS OF THE ALDEHYDES, KETONES, CARBOXYLIC ACIDS, AND CARBONIC ACIDS. AMMONO CARBONOUS ACID' W. CONARD FERNELIU~, THEOHIOSTATE UNIVERSITY,COLUMBUS. OHIO, AND WARREN C. JOHNSON, UNIVERSITY0s CHICAGO, CHICAGO, ILLINOIS

In the introductory portion of this article2 the formal resemblance of the simple nitrogen compounds of carbon to the familiar oxygen compounds of carbon was pointed out and a nitridation scheme was developed to show the interrelationships of these nitrogen compounds. In addition the ammono alcohols and ethers (the amines) were discussed in some detail. With this nitridation scheme in mind let us now turn to a consideration of the other substances represented there.

HC/NH

YHz

lr 1

HCN

HNC CzNo

Ammono Aldehydes and Ketones The aldehydes and ketones, characterized by an oxygen atom doubly bound to a carbon atom, form a definite and very interesting group of organic compounds. Similarly, the ammono aldehydes and ammono 'Previous articles in this series have appeared as fallows: I, THISJOURNAL, 5, (June, 1928); 11, IM., 828 (July, 1928); 111, Ibid., 6, 20 (Jan., 1929); IV, IbM., 441 (Mar., 1929); V, Ibid., 7, 981-99 ( M a y , 1930); VI, Part I, Ibid., 1291-9 (June, 1930). ' THISJOURNAL, 7, 1291-9 (June, 1930). 664

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LIQUID AMMONIA AS A SOLVENT

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ketones contain a carbon atom doubly bound to nitrogen. Here again the distinction between the two types lies in the presence or absence of a hydrogen atom attached to the carbon atom concerned. The aldimines and ketimines are thus ammono aldehydes and ammono ketones, respectively. ALDEHYDES

KETONES

At the start it should be stated that the relationships of the ammono aldehydes and ketones to the familiar water compounds, which are quite evident after a little study, are somewhat complicated because of the trivalence of nitrogen which makes possible a greater number of combinations than is possible in the case of divalent o x y g e ~ . ~ With this idea in mind it is seen that such compounds as CsHsCH=NH, although aldehydes because of the possession of a double bond, -CH=N-, also contain a hydrogen atom attached to nitrogen, in which respect they resemble the ammono alcohol^.^ These aldimines, therefore, should exhibit alcoholic properties and might well be termed ammono aldehyde-alcohols. As a matter of fact the hydrogen of the aldimines is readily replaceable by metals to give derivatives analogous to potassium ethylate,=

The acetals are derivatives of the aldehydes resembling on the one hand the ethers and on the other the esters. They are easily made by the interaction of an aldehyde, and an alcohol in the presence of anhydrous hydrogen chloride, CHsCH=O

+ 2CHaOH --+

CHsCH(OCHs)l

+ HzO.

Similarly, when an amine is used in place of an alcohol there is formed a substance which may rightly be termed an ammono acetal,

No such ammono acetals are known in the case of the primary amines; instead, there are formed substances of this type, CHaCH=NR, the Schiff a The nitrogen analogs of the well-known oxygen compounds are not to be regarded as being derived solely, as many have supposed, by the substitution of -NHs for -OH and =NH for 4 but rather, in the broader sense, as the substitution of trivalent nitrogen for divalent oxygen. 'Ref. 2, p. 1294. Strain, J. Am. Chem. Soc., 49, 1563 (1927). It might be said with equal justification that an aldimine possesses acidic rather than alcoholic -properties and should be called an aldehyde acid. Perhaps, as Bergstrom has suggested, it is better to compare ~

the aldimines. RCH=NH, to aldehyde hydrates, CClsCH(OH)2.

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JOURNAL OF CHEMICAL EDUCATION

JULY,1930

+

bases [CH3CH(NHR)2+CHaCH=NR RNH2]. These alkyl and aryl derivatives of the amines must be regarded as ammono acetals (because of the nitrogen to hydrocarbon radical linkage, =N-R) as well as ammono aldehydes (because of the double bond, -HC=N-) and may rightly be called ammono aldehyde-a~etals.~,' Upon the loss of ammonia, the imines are converted into hydramides,

These hydramines contain two true ammono aldehyde groups, -CH=N-, and one other group which is very similar to the acetals in that two valences of the central carbon atom are satisfied by two nitrogen atoms rather than by the same nitrogen atom. The hydramides then are 'further examples of aldehyde-acetals. Ketone-like substances other than the ketimines would be the following,

Polymerization.-One. of the outstanding characteristics of the aldehydes is their marked tendency to polymerize. Apparently such polymerization relieves the strain introduced into the molecule by the double bond between carbon and oxygen. Thus three molecules of formaldehyde readily coalesce to the familiar trioxymethylene ring and acetaldehyde forms metaldehyde and paraldehyde. When formaldehyde is treated with ammonia there is formed neither methylene imine, C H p N H , nor methylene nitride, (CH&Na, but instead hexamethylene tetramine, (CH&Nn, a dimer of methylene nitride. The closely parallel polymerization reactions are represented by the schemes,

and I t is interesting to note that according to these ideas pyridine, H C ~ \CH=CH is formally a cyclic ammono aldehyde acetal. Numerous reactions of pyridine support this hypothesis (Bermtrom. Swampseott Meetinp, A. C. S.. Sept., 1928). .. . . : R r c m s e of the re~ernl~lance~ which the aldimines hear to nlcohals and to acids. substances of thc type CslTsCII-NR might also bc callcd aldehyde ethers or ald~hydc esters although the term aldehyde-acetal is perhaps to be preferred.

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Because of the trivalence of nitrogen a simple ring is impossible so that a multi-ringed compound is formed of which the above is a plane projection. As ordinarily prepared, ethylene imine exists as the trimer (CHICH= NH)S.~ Addition Compounds.-The oxygen aldehydes have a marked power to form addition compounds with numerous substances such as hydrocyanic acid and sodium acid sulfite, C.HCH0 CsH.CHO

+ HCN --+ CaHsCH(CN)OH

+ NaHSOa --+ CIH~CH(OH)SOZON~

Similar reactions are known for the ammono benzaldehydes. For example, hydrocyanic acid adds directly to both hydrobenzamides and the Schiff hases,1° CsHsCH=N C~H&H< CsHsCH=N CsHsCH=NCeHs

+ 2HCN 4

GH6CH(CN)NH C~H~CH< C2H6CH(CN)NH

+ HCN +CHaCH(CN)NHCaHs

and sulfurous acid (moist sulfur dioxide) forms an addition compound with hydrobenzamide," C.H.CH-SOxOH

\

NH

C$HCH=N

\

CHCeHe

/

CsHaCH=N

+

2H2SOX

+

\

/CHCsHs YH

CaHrCH-SOnOH

'

Delepine, Compt. rend., 125, 951 (1897); 128, 105 (1899): Ann. chim. phys., [7], 16, 103 (1899); Bull. soc. chim., [3]21, 58 (1899). Plkhl, Ber., 13, 2118 (1880); 14, 1139 (1881). lo Cech, Ber., 11, 246 (1878). " Otto, Ann., 112, 305 (1859); van de Griendt, Thesis. Stanford University, 1926.

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Jmu, 1930

In the latter case, probably because of the formation of an inner ammonium salt, sulfurous acid itself forms a stable compound while only the salts are stable in the case of the aquo aldehydes. If a slight excess of water is added, the hydrobenzamide addition product hydrolyzes, forming two molecules of the addition compound of benzylidene imine. GH6CH(NH2)-

OSO.OH or CsHsCH

and one of benzaldehyde.

Oximes and Pheny1hydrazones.-Closely related to the formation of addition compounds of the aldehydes is the formation of oximes and phenylhydrazones. Hydroxylamine and phenylhydrazine react readily with the aquo aldehydes to form the characteristic reaction product and water, CeHsCHO

+ HnNOH+CsHsCH=NOH + HsO

The ammoho aldehydes react with these same reagents to form the same oximes and phenylhydrazones and ammonia in place of the water above. The following equations illustrate these reactions,

Reaction with the Grignard Reagent.-The reactions of the aldehydelike compounds of nitrogen with the Grignard reagent very strikingly illustrate their true nature. I t will be recalled that an aquo aldehyde forms an addition compound with a magnesium alkyl or aryl halide which may be subsequently hydrolyzed to a secondary alcohol.

The Schiff bases and the hydramides maJ: be utilized for the synthesis of analogous nitrogen compounds as is illustrated by the following equations,

Ref. 5, p. 1569. Ber., 37, 2691 (1904); ~ u s c hand Rinck, Ibid.. 38, 1761 (1905); Busch and Leefhelm, I. firakt. Chen. [2] 77, 20 (1908). la Busch,

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CsHsCHO

+2C

1607

+

H ~ H N H ~2BrMgOHX4 CzHa

Reduction and Nitridation.-Since the aldehydes constitute the first oxidation (nitridation) step beyond the primary alcohols, it is to be expected that the aldehydes would be capable of reduction to the corresponding alcohols. Such a reduction readily takes place in the case of hydrobenzamide. On treatment with a solution of sodium in liquid a m m ~ n i a , ' ~ benzyl amine is formed in abundant yield.le In alcoholic solution with sodium amalgam, hydrobenzamide gives benzyl amine and dibenzyl amine, both of which are primary ammono alcohols.'' Benzylidene aniline is also reduced by nascent hydrogen to a secondary amine which is a primary ammono alcoho1,'s CaHsCH=NC6Hs

+ 2H +CaHaCHp-NH-CaHr,.

Aldehydes are readily oxidized to the corresponding carboxylic acid, CHsCHO

+ 0 +CeH6COOH.

Similarly, benzylidene imine is nitridized to the ammonia analog of benzoic acid, benzamidine, by a liquid ammonia solution of i~dine.'g.~~ CHrCH=NH

+ HzNI +H I + C8HC(NH)NH2

Moreover, by the action of hydrazoic acid in liquid ammonia solution a t 100°, hexamethylene tetramine has been nitridized to guanidine--a reaction strictly analogous to the oxidation of trioxymethylene to carbon dioxide.21 Cannizzaro Reaction.-One of the most characteristic reactions of the aromatic aquo aldehydes is the Cannizzaro reaction in which equal quantities of an alcohol and a carboxylic acid are formed by treating the aldehyde with a solution of a strong base, "Busch and Leefhelm, J. @aka Chem., (21 77, 1 (1908). l6

For a discussion of a liquid ammonia solution of sodium a? a reducing agent see

THISJOURNAL, 6, 34 (Jan., 1929). Ref. 5, p. 1562. Fischer, Ber., 19, 748 (18%); Ann., 241, 328 (1887). '8 Schi5, Ann. Chem. Suppl., 3, 354 (1864). lo For a discussion of a liquid ammonia solution of iodine as a nitridizing agent. see THISJOURNAL, 7, 1298 (June, 1930). 40 Ref. 5. p. 1564. That a portion of the benzamidine deammonates to phenyl cyanide, benzoic anammonide, which for the most part polymerizes t o cyanphenine, (CaH6CN)8,the trimer of phenyl cyanide, does not invalidate the analogy. Franklin, "Reactions in Liquid Ammonia." Columbia Univ. Press. New York. 1927. l7


1608

2CsHsCH0

Jay,

1930

+ KOH --+ CsH.CH.OH + GH.COOK

Similarly, benzylidene imine, when heated with potassium amide (an ammono base) in liquid ammonia solution, undergoes intermolecular oxidation (nitridation) and reduction to give benzyl amine (ammono benzyl alcohol) and benzamidine (ammono benzoic acid), An interesting variation of this type of reaction is that between an ammono base and an aquo aldehyde in which an aquo alcohol and a mixed aquo ammono acid are formed,22 ZCsHaCHO

+ NaNHz --+ CaHaCH.OH+ CaHaCONHNa

Benzylidene aniline undergoes a Cannizzaro reaction although the products, acid and alcohol, are combined as an ester,23

Benzoin Condensation.-Benzoin is a substance formed by the condensation of two molecules of benzaldehyde in the presence of cyanide ion, CsHsCHO

--+

CsHaCHO

CsH6CHOH

I

GHsC=O

The reaction apparently takes place through the migration of hydrogen from the carbon of one -CHO group to the oxygen of another molecule and the establishment of a bond between carbon atoms. When hydrohenzamide is heated, an isomeric compound, amarine, results. Its formation may be looked upon, for the first step, as an example of a benzoin condensation because there is a shift of hydrogen from carbon to nitrogen and the establishment of a bond between carbon atoms,24 C6HaCH=N

CsH6CH--NH

C6HaCH=N

CsHsC=N

)CH-C~H~ --+

I

-

)CHGH~

CeH6CH-NH >.C~H& CsHsCH-N

I

When treated with an alkaline cyanide in liquid ammonia solution the Schiff bases, ammono aldehyde-acetals, undergo the benzoin condensationforming ammono benzoin acetals, such as benzoin-anil-anilide, as the following equation shows, Haller and Bauer, Ann. ckim. phys., [8] 16, 145 (1909). Kasiwagi, Bull. Ckem. Soc. Japan, 1, 66 (1926).

%'Strain, J. Am. Ckem. Soc., 50, 2218 (1928). Hurd and Bennett [J. Am. Ckm. Soc., 51, 1198 (1929)l have $4 Ref. 5, p. 1565. objected to this interpretation saying that the conversion of hydrobenzamide to amarine cannot be analogous to the benzoin condensation because of structural difficulties, and also because of the fact that benzoin is not a pyrolytic product of benzaldehyde.

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1009

The analogy does not stop here, however, for just as benzoin is oxidized to benzil so is benzoin-anil-anilide nitridized by a liquid ammonia solution of iodine to henzil-dianil, an ammono benzil,=s

The Carbazylic Acids Carbon, in the aldehyde-ketone stage of oxidation (nitridation or deelectronation) has two of its valences attached to oxygen or nitrogen. In that state of oxidation exemplified by the carbazylic acids, three of the valences of a single carbon atom are attached to oxygen. The formal nitrogen analogs of the carboxylic acids would he the amidines which might rightly be called carbaeylic acids especially

since they show acid properties in liquid ammonia solution.28 Acetamidine and benzamidine, two representative carbazylic acids, react, in liquid ammonia solution, with potassium amide as represented by the equation,

to form, respectively, a potassium ammono acetate and a potassium ammono Salts of the carbazylic acids are also formed by the direct addition of metallic amides to nitriles. For example, ethyl cyanide, which is the anammonide of ammono propionic acid, reacts with potassium amide, an ammono base, to f o m potassium ammono propionate just as propionic "Strain, J. Am. Chem. Soc., 51, 269 (1929). "The amidines are usually recognized as being basic substances. The basic nature of the amidines in the presence of water is due t o the formation of an addition compound with water which disswiates t o give hydroayl ion just a s does ammonium hydroxide. Thus, guanidine, a weak ammono acid in liquid ammonia solution, forms a very strong base in water solution, guanidinium hydroxide. Many acids which are unrecognizable as acids in aqueous solution have been found to show distinct acid properties in liquid ammonia solution because of the difference between the physical properties of water and liquid ammonia. Cf. THISJOURNAL, 5, 833 (July, 1928). Benedict, Thesis, Stanford University, 1924.

"

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JULY.1930

anhydride reacts with potassium hydroxide to form potassium aquo propionate. The parallel reactions are represented by the equations,

The one reaction takes place in liquid ammonia solution, the other in water. The potassium salts of palmitamide and stearamide, ammono soaps, behave like soaps in liquid ammonia solution in that they lower the surface tension of the solvent and promote frothing. Further evidence that the cyanides are to be regarded as anammonides of the carbazylic acids is furnished by the observation that methyl cyanide, heated in liquid ammonia with ammonium chloride, ammonates to acetamidine. The amidines are known to lose ammonia rather easily to form the corresponding cyanides. The close relationship existing between the carboxylic acids and carbazylic acids is further shown by such reactions as are represented by the equations, C H S x K

+ KOH --+

CH,

+ K2COa

Just as potassium aquo acetate when heated with potassium hydroxide yields methane and potassium aquo carbonate, so when a mixture of potassium ammono acetate and potassium amide is heated, methane and potassium ammono carbonate are formed.28 The alkyl and aryl substituted amidines are to be regarded as esters. Reactions illustrated by the following equations substantiate this view,

The first equation, a typical esterification, illustrates the formation of a diphenyl ester of ammono benzoic acid and ammonia by the reaction of an acid ester of ammono henzoic acid with an ammono alcohol and the latter illustrates the ammonolysis (saponification) of an ester of ammono acetic acid to ammono acetic acid and ammono phenyl alcohol. "Cornell, J. Am. Chem. Soc., 50, 3311 (1928). Bernthsen, Ann., 184, 349 (1876). Niemann. Thesis. Stanford University. 1926.

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The cyanides form with Grignard's reagents addition compounds, which upon treatment with liquid ammonia (ammonolysis), yield ketimines (ammono ket~nes),~' CaHsCN

+ GHsMgBr -+ C ~ H ~ CNMgBr J 'cs&

This synthesis'differsin no essential from the production of ketones through the interaction of acid anhydrides and Grignard's reagents,

Hydrocyanic AcidZ2 Because hydrocyanic acid bears a somewhat complicated relationship to the ammonia system it is necessary to consider this substance in some detail. The work of Nef leaves no question as to the existence of divalent carbon in the isocyanides and in hydrocyanic acid. Today, hydrocyanic acid is regarded as a tautomeric substance, HNC

* HCN

According to the first formula hydrocyanic add is an ammono carbonous acid and according to the second formic anammonide. It might also be expected that hydrocyanic acid would show the properties of an aldehyde since all of the valences of the nitrogen atom are attached to a single carbon atom just as all valences of oxygen are attached to a single carbon atom in formaldehyde (HCEN, H s C - 4 , the triple bond, -C=N, here being in a way analogous to the double bond, =C==O). The existence of this tautomerism is not surprising in view of the well-known tautomerism of the -011s acids of phosphorus, nitrogen, and sulfur, as represented by the following equilibria, ONOH SO(OH)1

= HNOp = HSOnOH

a Moreau and Mignonac, Compl. rend., 156, 1790 (1900); Ref. 28.

For a complete discussion of the relationship of hydrocyanic acid to the ammonia system of compounds and for complete references, see Franklin, I.Phys. Chcm.. 27, 1671 (1923).

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JULY.

1930

The surprising thing is that no similar tautomerism has been observed in the behavior of formic acid and formamidine (ammono formic acid). There remains to consider the evidence that hydrocyanic acid possesses the properties, first, of ammono carbonous acid; second, of formic anammonide; and, third, of an aldehyde. Ammono Carbonous Acid.-Carbon monoxide theoretically should be the anhydride of carbonous add.a3

In this connection it is interesting to note that sodium cyanide is formed by the action of carbon monoxide upon sodium amide, CO

+ NaNHg +C=NNa + H20

This reaction is in harmony with the view that hydrocyanic acid is ammono carbonous acid in that the reaction may be regarded as the formation of water (subsequently decomposed by the excess of sodium amide) and an ammono carbonite from carbonous anhydride and an ammono base. Hydrocyanic acid may be nitridized to the ammono carbonic acid, cyanamide, in liquid ammonia solution, NH4NC Jr H2NI --+

HN=C=NH

( ~ HsNCN) 2

+ NHJ

Similar nitridations involving the alkali cyanides are represented by the following equations, NaNC NaNC

+ NaN. +Na.NCN + N2 + N a N B +NaNCN + H?

These reactions differ in no essential from the oxidation of the cyanides to cyanates, 2NaNC

+ 0 . 4 ZNaNCO

Disodium cyanamide (an ammono carbonate) is reduced to.sodium cyanide by elementary carbon, NazNCN

+ C --+ 2NaNC

Finally, ethyl carbylamine (isocyanide) which is an ester of amnlono carbonous acid is saponified by potassium amide to potassium cyanide and ethyl amine (an ammono alcohol), GHsNC

+ KNH2

4 KNC

+ CzHsNH2

Scheibler's carbon monoxide diethylacetal, C(OC*H& [ B w , , 59, 1022 (192fi)l. may be regarded as the diethyl ester of carbonous acid.

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Carbonous nitride, CsN2,the end-product of deammonation of ammono carbonous acid is unknown.34 Formic Anammonide.-In support of the idea that hydrocyanic acid is the anammonide of formic acid, the following facts are offered: first, hydrocyanic may be converted (hydrolysis) successively into formamide and formic acid.

Second, formamidine hydrochloric is deammonated to hydrocyanic acid on gentle heating, HC(NH)NHrHCI

+HCN

+ NH4CI

Third, in the presence of hydrochloric acid and alcohol, hydrocyanic acid is esterified to an ester of mixed aquo ammono formic acid, HCN

+ C2H50H-+ HC(NH)OC2Ha.

Pourth, by the addition of the Grignard reagent and subsequent hydrolysis of the product formed, hydrocyanic acid may be converted into an aldehyde in the same manner as the closely related ortho aquo formic esters, RMgBr RMgBr

+ HCN +RHC = NMgBr 2 . RHCO + BrMgOH + NH,?

+ HC(OC2H& --+

GH80MgBr

+ RHC(OC2H&

34H60H

+ RHCO + BrMgOH.

Aldehyde Properties of Hydrocyanic Acid.-Assuming hydrocyanic acid to have the formula, HCGN, it is to be expected that this compound, because of its triple bond, nitrogen to carbon, and because of certain resemblances between the carbonyl and cyanogen groups, would exhibit aldehydic properties. As a matter of fact hydrocyanic acid shows conspicuously most of the properties characteristic of the aldehydes some of which are discussed below. I t shows the same strong tendency to polymerization as does formaldehyde, yielding a polymeric modification which reverts to the monomolecular form on strong heating. Hydrocyanic acid undergoes condensation in a manner strictly analogous to the familiar aldol condensation characteristic of the aldehydes, 2CH20 +CHzOH.CHO, 2HCN +CH(=NH)CN 4- HCN +HC(CN)ZNHX The "Stickkohlenstoff." (CaN&, reported by Pauly [Ber., 43, 2243 (1910)], CI-NI \cI, bas and obtained by the thermal decomposition. of tetraiodoimidazole,

11

-- &.

PT-NN

been shown to be a mixture of carbon and paraeyanogen (CIN9). [Wenzel, Dissertation, Stanford University, 19271. "Bodr&x. Compl. rend., 138, 92. 700 (1904).

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JULY, 1930

The triple bond between carbon and nitrogen as contrasted with a double bond between carbon and oxygen permits the reaction to proceed farther to a trimolecnlar condensation product. Sodium and potassium acid sulfites form compounds with hydrocyanic acid of the type, /S020K , which are obviously the analogs of the compound of the

HT:&

formula, H2C/OH , formed by the action of potassium acid sulfite on '~020K formaldehyde. Furthermore, hydrazine reacts with hydrocyanic acid in a manner essentially similar to its reaction with formaldehyde. The following equations represent these analogous reactions: HC-N

>

NH*

+ SHZN.NH2 + N . NHs + 2NHs HC=N. NHI HCO + H2N,NH* +H&=N .NH2 + H1O 2HCN

Ammono Carbonic Acidsa6 In carbonic acid all four valences of carbon are attached to oxygen. Therefore, those compounds in which all four valences of carbon are attached to nitrogen atoms should be ammono carbonic acids or derivatives of such acids. The formal relationships existing among the various ammono carbonic acids are shown in the scheme at top of the following page. The strong tendency to polymerize with formation of pyro acids and carbon nitrogen rings among the ammono carbonic acids-a power entirely lacking in aquo carbonic acid-renders the number of the ammono acids very large. The hydrolysis of calcium cyanamide as represented by the following equation, CaCN*

+ 3H10 +CaCOa + .2NH8,

admirably illustrates the relationship existing between the two types of carbonic acids since the reaction may be interpreted as the hydrolysis of calcium ammono carbonate to form calcium aquo carbonate and ammonia. It is also possible to reverse the above reaction by heating calcium carbonate in an atmosphere of ammonia. Furthemore, the ammono carbonic acids, guanidine, dicyandiamide, melamine, melon, and tricyanmelamine, on heating with water in sealed tubes for several hours are completely hydrolyzed to carbon dioxide and ammonia. All of these acids when treated with excess of fused sodium amide (a strong base of the ammonia system) are converted into disodium cyanamide. Dr. eranklin has discussed the ammono carbonic adds very fully, J . Am. Chem SOL.,44, 486 (1922). 3ee also, Burdick. Im., 47, 1485 (1925).

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Unknown ortho ammona Guanidine carbonic acid HN=C-NH~ >NH

Dicyanimide

1

I

HN=c

Liquid ammonia as a solvent and the ammonia system of compounds

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