Nomenclature of Organosilicon Compounds ROBERT 0. SAUER G ~ n e r o Electric l Company, Schenectady, New York In the preceding paragraph we have noted t h a t : ~ i ~ N ORGANOSILICON compound is a compound contammg . . a t least one carbon-silicon bond. ping referred to compounds of the empirical formula The first molecule of this type (except, of course, R2Si0 !R = an organic radical or hydrogen) as silisilicon carbide) was reported in 1863 (1)and the num- cones or polysilicones. This usage seems to have been ber of organosilicon compounds of known structure has based on a formal analogy with ketones in carbon chemincreased steadily, particularly since about 1900. istry; however, the analogy is an unfortunate one beMore recently this class of substances has begun to as- cause compounds of the formula R2Si0 have been isosume industrial importance. In view of (a) the present lated in only polymeric forms. Wohler' appears to use greatly increased interest in this field, ( b ) the possibility the term silicone to designate a compound of hydrogen, of existence of numerous and complex organosilicon silicon, and oxygen (of unknown structure, but presummolecules, and (c) the indefinite state of their nomen- ably containingsilicon-silicon,silicon-oxygen and siliconclature a t the present time, i t seems appropriate to hydrogen bonds). In this laboratory the term polydiscuss the development of the several schemes of silicone or, simply, silicone is used to designate high nomenclature now in use and to recommend some uni- molecular weight products of the empirical formula fying generalizations. These recommendations are RNSi0(4-.)/2 where N , the R/Si ratio, is less than three. the result of several years' actual contact with the In general, the exact structure of these polymers is unproblem of organosilicon nomenclatut-e and represent, known. I t is emphasized that this usage-which conit is believed, a considerable improvement in precision flicts with both the Kipping definition and Wohler's usage (and these conflict with each other)-is really an and euphony over existing terminology. Kipping was the first to feel the necessity for a scheme expedient extension of the Kipping terminology in order of nomenclature which could be rationally expanded to to classify a wide variety of organosilicon polymers and name compounds as yet unknown to him. He chose is not applicableto compounds of precisely known structhe root silicune for the simplest silicon hydride, SiH4, ture. Shortly after Kipping's proposal, Martin (6) sugand its derivatives (2). From this root the following compounds and group were named: HaSiOH, sili- gested the root names: "silicose" for compounds concanol; H2Si(OH)z,silicanediol; H3Si-, silicyl. For the taining silicon-silicon bonds, and "silicate" for comhigher silicon hydrides, e. g., SizHe,Si3Hs,etc., Kipping pounds containing the silicon-oxygen-silicon linkage. appears by his usage to prefer the names: silicoethane, These names were intended for organic as well as for silicopropane, etc., although he makes no definite inorganic compounds of silicon, but the proposal failed statement on the subject. In spite of the fact that he to become popular. Stock, who was active in the field of silicon hydrides, proposed the name silicanol for the compound HaSiOH and its derivatives, be consistently used the term silicol, proposed (7) the somewhat shorter root of silane (prowhich term appears to have originated with Ladenburg nounced sir-lane) for these compounds, prefixing this .. root in order to designate the number of silicon atoms (3). The intermolecular dehydration product of a silicol in the chain. Thus, SiH, was monosilane, H3Si(silicanol) was termed by Kipping a silicyl oxide, e. g., SiHs was disilane, and H & i S i H z S i H 3was trisilane. (CsHs)aSiOSi(CaH&, triphenylsilicyl oxide. The hypo- However, Stock did not rule out entirely the older thetical monomers derived by intramolecular dehydra- scheme by which alkyl silicon hydrides were named as tion of the silicanediols were termed silicones;' thus, silicohydrocarbons, apparently believing that it was (GH6),SiO was diethylsilicone. The products formed sometimes of value to preserve the analogy with by intermolecular dehydration of a silicanediol were familiar hydrocarbons. If all the carbon atoms of a named as derivatives of the parent diol by indicating hydrocarbon structure were replaced by silicon, this in thk name the number of molecules of water removed compound might then be designated according to and the number of silicanediol molecules condensing Stock as a "persilico" hydrocarbon. For example, to form the new compound. Thus, [(CBHS)2Si0]3, CH3SiHacould be named silicoethane as well as metbyla polysilicone, was referred to as trianhydrotrisdi- silane, and Si3H8could be persilicopropane as well as phenylsilicanediol and HOSi(CsH&OSi(CeHs)zOH as trisilane. anhydrobisdiphenylsilicanediol. Stock was also interested in the oxygenated derivaAccording to Mellor (4). "F.W6hler designated by the term tives of the silanes. The unstable monosilanol, silicone, a product which he obtained by the action of concen- H3SiOH, dehydrated yielding HaSiOSiHx, which Stock trated hydrochloric acid upon calcium silicide." This product termed (8, 9) disiloxane, that is to say, two silicon (5) was an oxyhydride of silicon, corresponding approximately atoms joined by one oxygen. Other compounds of to the empirical formula SirH102.
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this class which Stock named are: (HPS~O)~, disildioxane (two silicon and two oxygen atoms); and [(CsHs)~SiOlr, octaphenyltetrasiltetraoxane. The monomeric RzSiO from which these latter two may be considered to have been derived were designated as 0x0-monosilanes, the parent compound HzSiO, however, being termed "prosiloxane" ( 9 , l O ) . At this time, Stock sought to discourage naming silicon compounds according to the carbon analogs and to replace monosilanol with oxy-monosilane, monosilanediol with dioxy-monosilane and monosilanone with oxo-monosilane. In choosing a system of nomenclature or in devising a new one, especial emphasis should be placed on clarity, brevity, uniformity, and euphony if the system is to attain general acceptance. Our fust decision concerns the selection of the nomenclature root for the organosilicon compounds, this involving a choice between the terms silicane and silane. The latter is a shorter term and more adaptable to euphonious derivations than sificane although Kipping's root may perhaps enable more rapid recognition of the relation to the element silicon. As used by Kipping, silicane was not applied to compounds having silicon-silicon bonds, although this does not preclude our using the term disilicane for derivatives of Si2H8. The principal difficulty with the silicane root for everyday use is the length (an extra syllable) and consequent lack of euphony in the names of the derivatives. Kipping must have realized this, for although his proposed name for compounds of the type &SOH (R = an organic radical or hydrogen) was silicanol he used the term silicol in his publications. The more pleasing character of the silane root is easily demonstrated by repeating aloud the names of a few derivatives using both systems, e. g., diphenylsilanediol,dipbenylsilicanediol; silyl, silicyl; silanol, silicanol (or silicol). Another distinctive advantage to the scheme based on the silane root is its ready extension to compounds containing numerous silicon-oxygen-silicon (siloxane2)lmkages; this extension is overly clumsy using the silicane rcot. All in all, it seems as though silane should be the more widely used of the two roots; this is the one we have chosen. It should prove advantageous to omit Stock's prefix (mono) to this root for derivatives of SiHd. Thus, (GHs)&iClz becom,es diethyldichloro~ i l a n e ,but ~ (CH&Si--Si(CHa)a is hexamethyldisilane. The decision concerning the root having been made, the hydroxy silicon compounds are best named as -02s according to the Kipping system. Thus, (C2Hs)sSiOH is triethylsilanol and (C6Hs)&i(OH)2is diphenylsilanedioL2 The dehydration products of the silanols, variously referred to as siloxanes (pronounced sif-l6x-x-ane),silicyl oxides, or silyl ethers, are most advantageously named as siloxane derivatives. Since Stock assigned the term disiloxane to H3SiOSiHa, we shall refer to (GHs)sSiOSi(C2Hs)ras bexaethyldisiloxane. 'The recent paper of Hyde and DeLong (11) exemplifies the usage of this term.
This terminology is readily extended to compounds containing several siloxane linkages. For example, in naming silicon oxychlorides of the formula CUi[OSiCL].CI (where n = 1,2.3 . .) we shall designate the number of silicon atoms in the siloxane chain, that is, n 1, simply by the proper prefix to siloxane (omitting Stock's prefut to the -oxane ending). Thus, the compound ClaSiOSiClaOSiCla is called octachlorotrisiloxane. If the substituents on such a polysiloxane are not all of the same kind their number and position may be indicated by numbering the atoms of the chain and by using these numbers in conjunction with the appropriate p r e h and/or suffixto the polysiloxane root. For example, HOSi(CsHs)20Si(CsHs)zOHbecomes tetraphenyldisiloxane-l,3-diol. Cyclic condensation products of the silanediols can be satisfactorily described by merely prefixing cyclo to the same name one would assign if the molecule were linear. According to this system [(CdQzSiO]awhich Kipping called trianhydrotrisdiphenylsilicanediol-becomes hexaphenylcyclotrisiloxane. In naming compounds having branched siloxane chains, or siloxane rings with siloxane side chains, it should prove satisfactory to use the term siloxy- for the group RsSiO-. The radicals R3Si- and R,SiSiR2- may be termed silyl and disilanyl, respectively. The name for the latter was suggested by Dr. Austin M. Patterson, to whom this paper went for review, in order to distinguish the latter radical from two Rai-groups. By analogy with the siloxanes, compounds of the general formula R3Si (NRSiRz),R-where R has the same significance as before--are designated as silazines. Thus, according to this suggestion (CIHs)aSi-NHSi(GH& becomes hexaethyldisilazine, and CHIN= (SiH3)zbecomes 2-(or N-) methyldisilazine. It seems preferable to designate compounds of the type R3SiNRZ1as silylamines, e. g., HsSiNHCH8, N-silylmethylamine. At present, the nomenclature of the alkyl ethers (or esters) of the silanols, silanediols, and silanetriols appears quite inconsistent within the group. Compounds of the general formulas M i O R ' and R2Si(OR')2have been referred to as trialkyl(or ary1)monosilanol alkyl ethers and dialkyI(or aryl) monosilanol dialkyl ethers, respectively. Compounds of the general formnla RSi(OR1)a,however, have been termed trialkyl hydrocarbonorthosiliconates, e. g., triethyl methaneorthosiliconate for CHaSi(OC2Hs)3,or named as ortho esters of silico organic acids, e. g., ethyl orthosilicoacetate for CHsSi(OCzHs)s. One also sometimes sees a reference to esters of alkyl monosilane acids. The foregoing terms, though descriptive, are not selfconsistent. They also appear somewhat artificial since the silanetriols (acids?) in the case of the last example are unknown (12). It would seem more appropriate to include compounds of the general type KSi(OR1)r-,, (where R and R' are organic radicals and n may have the values 1,2,or 3) in the generic term silane and avoid inconsistency by naming the compounds mono-, di-, or trialkoxy(oraryloxy)silanes.
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In summary, the purpose of this paper has been to have been assigned using the current systems of discuss briefly the present situation of nomenclature in nomenclature, and these names are to be compared the organosilicon field and to select a scheme deemed with those suggested in the last column. reasonably precise and internally consistent. This system has been based on the following five generalizaACKNOWLEDGMENT tions. The author gratefully acknowledges the helpful criti1. aganosilicon compounds of the general formula cism of the several members of the General Electric reR [ s ~ ~ ~where ~ sR ~ may R ~be an organic radical, hydrosearch staff who have had occasion to use this system gen, halogen, an alkoxy or an aryloxy group and and is particularly indebted to Drs. W. I. Patnode, n = 0, 1,2, . . are named as silane derivatives. 2. aganosilicon con,pounds containing s i - - o ~ i E. G. Rochow, and IN.M. Sprung for valuable suggestions during the evolution of the views presented here. linkages are named as siloxune derivatives. 3. Organosilicon ring compounds of the general LITERATURE CITED formula [R2SiO], where R has the same significance as in 1 and n = 2, 3, 4, . . are named as cyc~osi~oxanes. (1) FRIEDELAND C~~ms,Ann., 127,28(1863). (2) KIPP'NG.PIOC. Chem. Soc., 28, 243 (1912): J. Chem. Sac., 4. In organosilicon compounds containing one or 101,2106-7 (1913); C. A., 7, 976 (1912). more hydroxyl groups attached to silicon the name is (3) LADEmmc,Ann., 164,316!319 (1872), (4) MELLOR, "A Comprehens~veTreatise on Inorganic and formed by adding the suffixes -01, -dial, -trial, etc. Theoretical Chemistry," Longmans, Green and Co., (corresponding to the number of hydroxyl groups per London, 1925,vol. 6, p. 231. molecule) to the proper root name (see 1 , Z , and 3 ) . (5) WOHLER, Ann.. 104,374(1857). (6) MARTIN, PIOC. Chem. Soc., 29, 190 (1913); C. A,, 8, 3294 5. Organosilicon compounds of the type formula (1914). R[SiRzNHl,SiRs where R has the same significance (7) SrocK,Ber,,'lP, (1916), as in 1 and n = 1 , 2 , 3, . . . are named as silazine deriva(8) STOCK, ibid., 50,169-70 (1917). (9)STOCK, ibid., 1769-70 (1917). tives. Table 1 lists a few of the simple known compounds ~ ~ ~ ' 9.9i2 ~ ~ Sot,,d 63,1194 i (1941), j ~ representative of the types under discussion. Names (12)S~oc~,Ber.. 50,176 (1917).
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TABLE 1 Coarpmsoa os rns S s v ~ aN ~O , X B N CSTWBYS L.~~~B
01kr usngc Trimethylethyl silicon Dimetbyl d i c o o dichlotide
niethy~aricand Diphenylsilicanediol Triethyldicyl oxide
... .. . Triethylsilylefher ...
Triethylailicol
~
~
