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RESEARCH MEMO M
CALCULATED HJWTS OF FORMATION AND COMBUSTION
OF BORON COMPOUNDS (BORON, HYDROGEN,
CARBON, SILICON)
By Aubr ey P. Altshuller
Lewis Flight Propulsion Laboratory Cleveland, Ohio
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GRADE OF OFFICER MAKING CHANGE
NATIONAL ADVISORY COMMITTEE
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AERONAUTICS
WASHINGTON
October 4, 1955
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AERONAUTICS
CALCULATED HEATS OF FORMATION AND COMBUSTION OF BORON
cowom (BORON, HRocxN, CARBON, SnICON)
By Aubrey P. Altshuller
SUMMARY
The heats of formation and couibustionhave been calculated for liquid and gaseous alkyl- and silyl-substitutedboron compounds by a semitheoret-
. (^) ical method. (^) Alkylation and more especially silylation (substitution of a SiH3 group) reduce the heat of cotiustion. As the molecular weight of
a- the parent boron hydride increases, the reduction in the heats of cotius- =! (^) tion resulting from the substitution of a given number of al@l or silyl L (^) groups decreases. As many as three csrbon atoms can be substituted on
boron hydrides with five or more boron atoms without reducing the heat of couibustionbelow 25,000 Btu per pound. (^) The substitution of one silicon atom reduces the heat of couibustionas much as do three carbon atoms. Alkyl-substituted higher-molecular-weightboron hydrides may prove to he satisfactory high-energy fuels.
INTROIXJCTION
Considerable effort has been put into the synthesis and investigation of the physical, thermodynamic, and kinetic properties of”liquid and solid fuels containing boron and hydrogen, or boron, hydrogen, and csrbon (refs. 1 to 15). These boron-containing fuels have heats of combustion as much as 70 percent higher than JP fuels (ref. 7 and this report), high flme speeds (ref. 8), and high specific impulses (ref. 9)jconsequently, they afford high thrust and improved range for ra-jet and rocket applications.
Experimental determinations of the heats of combustion of boron- containing compounds are complicated by the incompleteness of combustion of the boron and carbon (refs. 10 and 11 and unpublished Lewis data). Fut&rmOre) it is very difficult to prepare boron hydrides or alkylated boron k@3rides of high purity and maintain such purities over appreciable periods of time (unpublished Lewis data). (^) However, the experimentally .- (^) known heats of formation available for several boron hydrides and tri- alkylboranes can be used along with the appropriate bond energies to +.
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1,1,2-TMmethyldibrsme
~3\ /~
. /~B\
‘3 H
siH3\ siJ ,~B< 1,1,2-K&isilyldiborane siH3 H
The name boryl for the BH2- radical suggested in reference 16 is adopted as are the nsmes methylboryl snd dimethylhoryl for (CH3)BH- =d (CH3)2B- respectively. (^) Compounds of the types R2BCH#R2 sad ~BqH4~ will be named in the following way:
H2BCH2BH2 Diborylmethane
H2BcH#H2BH2 1,2-Diborylethsne
H2B@2BHCH3 Borylmethylborylmethane
CH3BBCH2BHCH3 Bi s-methylborylmethsne
H2BCH2CH2BHCH3 l-Boryl-2-methylborylethane
(CH3)2Ba2C~B( CH3)z 1,2-Bis(dimethylboryl)ethane
The radicals formed by removal of a hydrogen atom from the boron hydrides other than borane will be given the anyl ending. Thus, the radicals B5Hs and BIOHU wilL be referred to in the present report as the pentaborsnyl sad decaboranyl radicals. ConsequediLy, alXylated ad silylated derivatives of pentaborane and decaborsme may be named as sub- stituted hydrocarbons sad silanes, but more comnon usage calls for naming these compounds as alkyl and silyl derivatives of the various boron hy- drides. When two radicals are joined, as in B5H8B5H8, the b i prefex will be used as in biphenyl C6H5C6H5. Since the thermochemical information is insufficient to differentiate thermally between nonequivalent boron atoms in pentaborane and will not be used.
‘5H8H
B5H# iH
decaborane, the numbering of the skeletal boron atoms To illustrate,
Methylpentaborane, or pentaboralmethane
Silylpentaborsne, or pentaborsnylsil.ane
.
,.--. -——.
-.
,. ..-.
B5H8C2H
B5H~B5H~
B5H~cH~B5H~
B5H~cH#H#5H~
B~~H13cH
%O=13%OH
B10H13CH2CH2B10H
Ethylpentabor,me,
Bipentaboranyl -.
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., or pe~a%oranylethane (^) .- .- -..: --- (^) .,! .-... ., ; _— .,^ — Dipentaborany@etha~ _. .— ‘lj2-Dipentaboranyle~hsn~ (^) ..
Methyldecaborane, or decaborsnylmethsne (^) ,.
Bidecaboranyl ~ X .-^ ,- — (^) ,, 1,2-Didecaboranylet~ane’--. .-..-i,,.
HEATS OF FORWTION OF BORON HYDRIDES,
SILYZ RADICALS, AND GASEOUS
.—
TRIALQiBotis, AIKYL AND
BORON.@D -ON (^) 1,
The heats of formation of di’boraneB2~, peri~aboraneB5~, snd deca- borane B10H14 have been determined at the ~~tion+ B@eau of Standar@ ~: ‘“ ~ref. 6) from the thermal decomposition of.the hy@ri==s to boron snd hy- drogen. These values are listed in table I. The heat of formation of borsne BH3 listed in table II was calculated from the heat of reaction—-.
of 28 kcal.per mole for the reaction B2H6+2BH3 (ref. 13) and the heat of formation of diborane. The heats of formation O! B2~5j B2H4, B2H3~ B2H2~ B5H8~ ~d B10H13 in table II have been estimated~y assuming that the bond— dissociation energy for breaking the first.~oron-to-hdrogenb ond so as to form B2H5~ B5H8~ =d B10H13 ~d the average boro+hy~ogen bond energy in forming B2H4, B2H3j and B2H2 may be approximated ~Y ~he average boron=to- hydrogen bond energy in borane. This assumption !wi.11be discussed in more detail in the following section on bond energies.1 ~~ ::,. -.. . The heats of combustion of the trimethyl-, tkiethyl-, tri-n-propyl-,
and tri-~-butylboranes have been determined (refs:.6;’10, and 15). Complete combustion of boron-containing compounds!(refs. 10 and 15) “ is difficult to obtain. Residues of both boron dad csrhon and possibly psrtially oxidized products also often remain aft@ ccmibustion. Although the residues may be partially corrected forby analy=is (unpublishedLewis data), the uncertainties in the experimental heat% of:combustion at present- range from *1 to *2 percent. (^) As,a consequence, t~e &ats of formatiti of the trialkylboratis are uncertain from +5 TO ti5 kcarper mole. — ““
—- (^). ---
.- -witm33w i : NACA RM E55G
BH3(g)+B(g) + 3H(g) ~
and ,—^ —^ --..=
BR3(g)+B(g) +-3R(g) (^) i :— ;. ;!,.~-
where R is alkyl radical. Similarly, the experime&l average bond energies may be obtained for the carbon-hydrogen &@6ilicon-hsilrogen ‘-
..
n .“ ., :
.
. ,=.. ,. — (^) ,. .
— bonds from the dissociation processes - 1. i =-- - .- “ -=-. 3-
and
.,.. ;=.. ,, I! ,—
SiH4(g)+Si(g) +~(g)! j (^) .- 1~:
Another method of obtaining average bmd ene~gie~ uses Paulingls- ,. equations (ref. 22) involving the srithmet~c and georn~tricmesns of tlie^ ~ nonpolar bond energies. The equation involving t~e geometric mean is.. , more satisfactory to use and has therefore,been eq’iplo~edto calculate the’” average bond energy for the boron-silicon bond fo< which no experimental data ae available. This equation is Z
D=(Y-z) = d
D(Y-Y)D(Z-Z) +“:23.06[;Y-:”~]
Wher; D(Y-Y) and D(Z-Z) are nonpolar bond energies,-that is, D(C-C), D(C1-C1), and,so forth; Xy and Xz are the electronegativities of ‘~ atoms Y and Z (ref. 22). The D(B-B) and XB ~havebeen obtainedby ‘ solving simultaneous ,(Eauling)equations using da~a f& the boron com- poundp@H3, BBr3, and BR3, where the heats of fo~at~on, D(H-H), D(Br-Br)’~ D(C-C)~ xH> xBr> and Xc, are known. The value o~,. D~B-B) also has been.- determined by solving the simultaneous equ@ions ~nvoTved in the decorn~o- Sition reactions for BH3, B2H6, B5H9, and E10-H14.~ The rnuibersof the various types of bonds (B-H, B-B, BHB, BBB) sre taken-from reference Es”.‘ The average values obtained for D(B-B) and^ xB^ be^ PO^ kcal per mole,.an~~ 2.0 units, respectively. (Pauling (ref. 22J previous_Jyobtained an xB of 1.95 using more limited data.) These values mdy then be substituted back into Pauling~s equation to obtain SUCQ bond energies as ~a(Si-B).
All the pertinent average bond energies obtZainedexpe~imentally-or fram pauling’s equation are listed in table 111.;. : Q.
-.^ ,— J-
. (^). — .. “ .- -+
... — ,.
.-—.
——
— -. ..— -- .
.—.-.
Actually bond dissociation energies such as (B5H8)-H are desired, not average energies. For exemple, by use of the average%ond energj ~(B-H)
, -’ —-..^ _^ A
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.
l
in pentaborane, the assumption is made implicitly that all boron-hydrogen bonds have equal energies. Furthermore, it is assumed that the apex boron in B5~ is the same as the base Wren atom (ref. 3). Similarly, the four different types of boron atom in decaborane (ref. 3) are assumed to have equal D(B-H) values. (^) Unfortunately, no bond-dissociation-energy data for specific dissociations ~~i-H sre available for boron hydrides. When more detailed information on bond energies and bond dissociation energies of boron hydrides does become available, it may become possible to esti- mate the differences in boron-h@ogen bond energies smong nonequivalent boron atoms in the higher boron hydrides.
METHODS OF CAKX%WTION
Heats of Formation
The heats of formation of boron-containing molecules for which there are no experimental data from heats of co?ibustionyheats of decomposition, and so forth, can now be computed. The method to be used involves atomiza- tion or dissociation reactions. For exsmple, methylpentahorane (or penta- borsnylmethsne) B5H8CH3 maybe (1) atomized into gaseous atoms or (2) dis- sociatedby breaking a single boron-carbon bond as follows:
B5H8~++=(g) + c(g) + ~H(g) (1)
B=jH@@+B#@) +cH3(d (2)
Where possible, the molecules of interest willbe dissociated (eq. (2)) into boron hydride fragments such as gaseous pentaborsne and alkyl or silyl radicals. For the alkylated diborylmethanes, diyentshorsnylmethane, and didecahoranylmethanes, decompositions to gaseous carbon sJ.sosre in- volved. In such cases csre was taken to use the appropriate values for aversge csrbon-hydrogen snd boron-carbon bond energies (table III).
The heats of these dissociation reactions are taken as the sums of the bond energies for the bonds broken in formation of the fragments. Thus, in the dissociation reaction for B5H8H3(g) given in equation (2)J one boron-carbon Just 89 kcal per
In general,
bond is broken; therefore, the heat of dissociation is. mole.
the heat of formation
‘f = @,(products ) -
@f willbe given
~(dissociation)
by
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Oxide
H20(g) B203(cr@alline ) B203(aorphous ) C02 (g) Si02 (smorphous)
Heat of formation (at 25° C), @, kcallmole
The heats of formation of water vapor and of carbon dioxide sre accu- rately known (ref. 21). The heats of formation of crystalline and amor- phous boric oxide (ref. 6) probably still are uncertain to M. kcal per mole. The heat of fOI’matiOnof amorphous SiMCa iS used (refs. 24 and 25) because X-ray analysis shows that the silica resulting from bomb calori- metry of silanes is amorphous (ref. 26). . 0 !=! Heats of formation and couibustionappear in table V^ for substances in & the liquid, solid, or gaseous state.^ Heats of cotiustion were^ calculated for reactions yielding both amorphous and crystalline boric oxide as prod- ucts. These values have uncertainties of MOO to MOO Btu per pound.
The heats of conibustionof the various series of boron compounds are plotted in figure 1. Only the heats of cmibustion of the liquid boron compounds oxidized to B203(smorphous) are plotted in these figures. How- ever, as can be seen from table V, the heats of cotiustion for the gaseous compound sre only 100 to 300 Btu per pound higher than those for the same substance in the liquid state. (^) The vslues plotted represent the lowest heats of contxzstionof those listed in tsble V. The most favorable heat- of-combustion values, which me for the boron compounds in the gaseous state oxidized to B203(crystalline), are 100 to 700 Btu per pound higher.
DISCUSSION OF RESULTS
The heats of couibustionlisted in table V ad plotted in figure 1 provide data from which a ntier of interesting conclusions can be drawn. The effects of @lation or silylation of a given boron hydride and on different boron hydrides now maybe examined in detatl.
. Triallcyl-and Trisilylboranes
= Alkylation and silylation have a^ cormnon^ detrimental effect on the heats of conibustionof the psrent boron hydrides. Alkylation of borane
J
,z - +
10
. :< NACA RM E55G26 ‘--“:
. .. to form R@ compounds reduces the heat of combustion .toa range of values,,_.. only 10 to 20 percent higher than those fo~ JP fuels ‘(AH. for JP fuels,.U. . from 18,000 to 19,000 Btu/lb). Silylationto fo~ heat of combustion below that of most hydrocarbons l(a)).
Alkyl- and Silyldi’boranes’
B(SiH3)3 reduces the ““ ‘: ~-”; (see table V and fig. — ;,^ .= —-—z
-..^.^ ,, ,- ., While diborsne has a heat of cofiustion of more >han 31,000 Btu ~er ~ pound, the heat of combustion of [email protected] 4700 Btu per pofid” (^) G lower. Further all@ation lowers the heats of co$bus-ti.onto between
20,000 and 24,000 Btu per pound. The rnonoalkyldifioranessre unstable titk- respect to rearrangement to di- or trialkyldibora$es.– (^) ,:.=——.— , Silylation of diborane, even monosilylation,~.dr~ticallydepresses
the heat of combustion. The heat of combustion 0$ monosilyldiborsne is
as low as that of trimethyldiborane and the heatslof .conibustionof tri- ‘ .. and tetrasilyldiborane are no better than those of’J!?fuels (table V fid’””“- — fig. l(b)).
AlkY1- and Silyltetraboran~s “; —. . The heat of combustion of tetra%orane itselfiis_ml.y 600 Btu per
pound less thsm that of ddborane and is about 140f)Btu per yound higher. than that of pentaborsne. Although the heats of omb~stion fall off ““ “ more rapidly with alkylation and silylation of te rabor~et than penta- “-
borane, the higher initial heat of combustion of }heprent compound “’ ‘“- ‘-
tetraborane results in a higher heat of conibustiopfo< all the alkylated
–A
and silylated tetraboranes considered when.compared with the correspond-
ing slkylated or silylated pentaboranes (see foil wi~ section). Although ‘- tetraborane itself is rather unstable, the slkyla,ed or silylated deriva-”t tives might possiblybe appreckblym ore stable (~abl~V and fig. l(c)). ti -.ti=
. k AIJcyl-and Silylpentaborsne& ~
A.lkylationof the heavier pentsborsne,molecu~e has less-drastic con- sequences on the heat of combustion than alkylati~n @es for diborsne. The methylpentaborane (or pentaborsnylmethane) hap a-heat of cotiustlon “ only about 2100 Btu per pound lower than does pen$aborane itself’. Even propylpentaborane (or pentaboranylpropsne) has a heat of combustion of about 25,000 Btu per pound, which is quite:an apy!reci~blegain over ~-- ‘; “’ fuels. Silylation again causes a much larger dep&esfi30nin the heatti-of combustion than does alkylation. Silylpentaboran& (or pentaboranylsl~me) with only one silicon atom has a heat of combusti~n ~out the stie”asia% of propylpentaborane with three csrbon atoms (teb}e ~and fig. l(d)). (^) II —.
., !--
— 1 —.
— (^) ... --.. .-
12 1- NACA Ri””E55G ,—.
to 28,000 Btu per pound (table V and fig. l(g)). ~Their heats of combus-’” “ tion appear to be slightly higher than the methyl’an<ethyl derivatives of penta’boraneand &ecaborane. The didecaboranylalkanes~have heats of Cornbus- tion as high or higher than the dipentabortinylalkane<with the same n~%qr of carbon atoms. If the 3iquid dipentaboranyl- a~d didecaboranylalkan.es could be prepared, they might be very satisfactory high-energy fuels. Even higher dipentaboranyl- and didecaboranyltiaues~ such as 1,2- “. didecaboranylbutane, should have quite high heatslof -combustionin the range of 25,000 to 26,000 Btu per pound (estimatedby extrapolation) and may have very satisfactory liquid ranges, low vol@il_Xties, and fairly ““ high densities. I (^) ‘-— .:
Heats of Combustion of Isomers
It shouldbe noted that many of the compoun@ mentioned in this re- port can have a number of isomers. For example, $he “SJ_kylgroup in an alkylpentaborane could be attached to either the @pef”or the base boron ~:...: atom in pentaborane. Again, in Mpentaboranylmet@ane, the two pentaboranyl= radicals could be joined by the methylene group al>exto apex, apex to base, or base to base. Quite probably these isomers haye somewhat different heats of couibustion. The present status of thermochemical.knowledge of ~~ .._ boron compound6 does not justify the refinement of estimating the Mffer- ences In the heats of formation of isomers, and cchsequently, in their heats of conibustion. 1 —-.^ :,
CONCIIJDINGREMmK8:. ,::
The present calculations of the heats of cotiustion of alkylated and silylated boron hydrides indicate that alkylated derivatives of penta: .:.. borane and higher boron hydrides should be among the best high-energy fuels. The higher the boron content, the less all&lation will affect the heat of couibustionof the boron hydride. However; it is also possi%le that considerable alkylation wouldbe necessary to obtain a liquid fuel from a compound such as bidecaboranyl. The preptiati~n of compounds such as B5H8(~2)nB5H8 ~d B10H13(CH2)nB10H13 might result..invery satisfac~o~ liquid fuels. However, further synthetic work is ,necesssrybefore the exact nature of the best or several best boron-containing high-energy fuels can be specified. ~=.. As more accurate and extensive thermochemical.data become available for boron hydrides and alkylated boron hydrides, ~al.~lations of the t~e made here also can become more accurate and extendive. b view of the experimental difficulties involved in the thermocl@i@ry of ,boroncom- pounds, the procedure of using a small amount of experimental data as a ..._ ba@e from which to make extensive semitheoretical.!cal@lations will yob- ably be of vslue for some time to come. 1-
& ,- —
. (^) — --
— -+
— ..r .— —
— =..
.
—
~ — ~
I :.
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.
It also wst be remetiered thst most of the compounti for which csl-
. culations sre made in this report have^ never^ been prepared.^ Furthermore, many of these conrpoundsmsy be very unstdle and undergo decomposition, rearrangement, or polymerization reactions. The answers to such questions of stability amit further synthesis work and physicsl measurements.
.
.
.
m
The vslue of a given compound as a fuel is determinedly a nuxber of other considerations besides its heat of conibustion. A compound may have a desirshle heat of cotiustion but an unsatisfactory liquid range. A^ 10SS in heat of combustion through alkylation may result in a fuel which has a wide liquid range and also better handling characteristics. Further- more, a higher co?ibustionefficiency, obtained by allsylationor possibly silylation, may compensate or more than compensate for the loss in heat of coxibustion.
obviously, all the factors mentioned and perhaps others WSt be bal- anced against each other in obtaining the most desirable fuel. A boron- conttining fuel is yrobably undesiz%ble if it has a heat of co?ibustion no higher or very little higher than those of JP fuels. The exception might be aboron fuel which is being used for its high flame velocity and high thrust rather thsm its high heat content. However, most of the boron fuels with high heat contents slso probably have high flame velocities and thrust; thus it appears that use of a low-heat-content boron fuel would rarely be advantageous.
SUMMARY OF RESULTS
Estimation of the heats of conibustionof several families of sMcyl- and silyl-substitutedboron hydrides shows that
- Al@lation and especially silylation (substitution of SiJ13groups) of boron hydrides decrease considerably the heats of conibustion.
- As the moleculsr weight of the psrent boron hydride increases from borane to decaborane and then to bidecaboranyl, the depression in the heats of conibustionresulting from the substitution of a given nwn- ber of csrbon or silicon atoms decreases.
- The heats of conibustionof by alkylation to vslues only 10 to fuels.
- The heats of combustion of rapidly reduced by substitution of diboranes have heats of cotiustion 19,000 Btu/lb).
borane and diborane me rapidly reduced 20 percent higher than those of W
borane and diborane sre even more silyl groups. The tri- end tetrasilyl- very near those of JP fuels (about
NACA RM E55G26 15
.
.
Upscomb, W. N. : (^) Structures of the Boron Hydrides. Jour. C&m. Phys., vol. 22, no. 6, June 1954, pp. 985-988.
Shapiro, I., Iandesman, H., sad Weiss, H. G.: Boron Q@ride Program at NC%CS. Third Eght Metal B@5_de meeting, Dept. Defense, Res. and Dev. Board, Conmd.tteeon Fuels and Lubricants, Mar. 4, 1953.
Schubert, A. E.: General Electric Company Boron Hydride Program. Third Light Metal Hydride meeting, Dept. Defense, Res. and Dev. Board, C!cmmdtteeon Fuels and Lubricants, Mar. 4, 1953.
Whgman, Donald D., Munson, Thomas R., Evans, William H., and Prosen, Edward J.: Thermodynamic Properties of Boron Compounds. NBS Rep. 3456, U.S. Dept. Commerce, Nat. Bur. Standards, Aug. 30, 1954.
Joyner, P. A., Adams, R. M., and Galbraith, H. J.: Methods of Esti- mating Heats of C!ambustion. Rep. No. CCC-1024-TR-3O, Callery Chem. Co., June 30, 1954.
Gammon, Benson E:, Genco, Russell S., and Gerstein, Melvin: APre- Hminarylhrperimentsl and Analytical Evaluation of Diborane as a Rsm-Jet Fuel. NACARME50J04, 1950.
G-on, Benson E.: l?re~nary Evaluation of the Idr and Fuel Specific-l@ulse Characteristics of Several Potential Ram-Jet Fuels. III - Diborme, Pentsborane, Boron and Boron - Octene-1 Slurries. NACARME51D25, 1951.
- Long, L. H., ad Norrish, R. G. W.: The Strengths of Certain Con- valent Metal”Bonds. Phil. Trans. Roy. Sot. (London), ser. A, vol. 241, no. 838, Apr. 26, 1949, pp. 587-617.
- Waszeciak, P. H., and McCarthy, E. R.: (^) Determination of Heats of Combustion of Compounds Containing Boron. MCC-1023-TR-9, Tech. Res. Rep., Matbieson Chem. Corp., Dec. 17, 1953.
- Wallenstein, Merrill B., and Frosen, Edward J.: Bond Energies and Heats of Formation of Sme Boron Compounds. NBS Rep. 3455, U.S. Dept. Ccmmerce, Nat. Bur. Standards, June 30, 1954.
- Shepp, AJJ_an,and Bauer, S. H.: (^) Computation of Entropy ~crements in Gaseous Bimolecular Associations. I - Donor-Acceptor Reactions. Jour. Am. Chem. Sot., vol. 76, no. 1, J-. 5, 1954, pp. 265-270.
,.. (^) _? .;
!,. .-—.-
(^16) NACA RM E55G
14.MaIIn,D. J., Schaeffer, P. F., and Irgon, J.:; H&h Energy Solid _
15 l
Propellant Investigation. Rey. N-486 -Sl,!S~-Annual Rep. Jan. 1 to June 30, 1953, Reaction Motors, Inc., @pt. 4, 1953.
Tannenbaum~ Stanley? and Schaeffer, Paul F.:~ T@ Heat of Combustion of Tri-~-butylboron. Jour. Am. Chem. Soc.j vdl. 77, no. 5, Mar. 5, 1955, Pp. 1385-1386. ,^
Schaeffer, G. W., and Wartik, T.: llbstracts~of->heKansas City Meeting of the American Chemical.Society, @r. 1954. (^) ----
Stevenson, D. P.: Ionization and Dissociation by Electron impact Of Normal tieS, C4-C8. The Dissociation Ri,~rgiesof D(n-C3H7-H) and D(n-C4Hg-H) and the Ionization Potenti@ of n-Propyl Radical. Trans. Faraday Sot., vol. 49, 1953, “pp. 86:7-878.
Kistiakowsky, G. B., and Van Artsdalen, E. R!: .~”rominationof Hydro- carbons. I - Photochemical and Themal B@mination of Methane and Methyl Bromine. Carbon-Hydrogen B~d Stre@@h tn Meth~e. JOWO ., __ Chem. Phys., vol. 12, no. 12, Dec. 1944, p]?.469-478. (^) ,,..
Andersen, H. C., sad Van Artsdalen, E. R.: @[email protected] of Hytio- carbons. II - Photochemical Bromination of Ethane and Ethyl Brmnine. Carbon-Hydrogen Bond Streqgth inlEt@ne. Jour. chem~ Phys., vol. 12, no. 12, Dec. 1944, pp. 479!-483f
Leigh, C. H., and Szwarc, M.: The Pyrolysis,of ri-Butyl-Benzene~d,,. the Heat of Formation of n-propyl Radical.” Jour. Chem. Phys., vol. 20, no. 3, Mar. 1952, ~. 407-411.
Rossini, Frederick D., et al.: Selected Values of Chemical Thermo-. dynamic Properties. Circular 500, Nat. B@.^ Standards, Feb. 1952.
. ,- Paulllng,L3nus: The Nature of the Chemical pond.^ Second cd., CorneJl Univ. Press, 1940.
Eberhardt, W. H., Crawford, Bryce, Jr., and ljipscomb,William N.: The Valence Structure of the Boron Hytiide$. Tour. Chem. Phys., “ vol. 22, no. 6, June 1954) PP. 989-1001.
Humphrey, G. L., and K3ng, E. G.: Hedts of ?’o~tion of Q~rtz ~L Cristobalite. Jour. Am. Chin. Sot.; vol. 74, no. 8, Apr. 20, 1952, pp. 2041-2042. ,--^ !F
Thcunpson,Raymond: Heats of Combustiorisnd ~ormation of Some Line~ Polydimethylsilonnes; the Si-C and”Si-O B@d--ergy Temns. Jour., Chem. SOC.) pt. 2, 1953, Pp. 1908-1914.^ ~^ ‘..—
—-
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18 NACA RME55G
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.. e’ (^) ; TABLE I. - EXPERIMUWU HEATS OF FORMATION OF BORON
HYDRIDES, TRULKYIEO lVJYES,AND G$?J30US
CARBON AND BORON ATOMS!
[Temperature, 25°.C] I ~
Substance Heat of formation, 4 : REference kcaL/mole .. Liquid (^) Gas
‘2H
--- 7.53 ~.^6
B5H9 7.8 15.0 ~ 6
%0%4 8(crystalline)^26
I
(CH3)3B -34.5 * 3.5 -29:3 + 315,.. -^ a~b (C2H5)3B -46.8 k^ 4.7^ -38.0 k 4:7^ a -23 i.8 -148 ~ (^) (c) (@3H7 )3B -65^ -54^ ‘ -40 ~ (^8) -298 : (c) (~-C4H9)3B -83.9 t 4.2^ -70.8 *^ 4!,2^ a -94 -81 (^15)
c O(graphite) 171.7 : (^21) B O(crystalline) 141*5 ~
SI O(crystalline) 100 * 10 , 4:)
aprlvate communication from W. H. Johnkon~& E. J. Prosen, Nat. Ikur.Standards. (^) i -;’ b Values of ~(l) and AH;(g) calcula$edlrom data in refs. 10 and 6 are essentially the sake as Nat. Bur. Standards values. (^) .- cUnpublished Lewis data. .-. interpolated from experimental de,taml (d~H5)3B and (3-C4~)3B. 1- +-.—
‘Average value from data of ref. 27. ~ –
--
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. — — (^) ..-. (^) —
—^ I — ,- .— :.. - (^) = .— .
,. ..
-.^ :“ ,,
NACA RME55G
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TABLE II. - CALCULATED KEATS OF FORMATION OF ALKYL AND SILYL RADICALS
AND UNSTABLE SPECIES OF BORON HYDRIDES A.NDALKYLNTED BORON HYDRIDES
[Temperature, 25° C]
Substance (^) Heat of forn?ation, ~, (^) Calculated from data in (gas) (^) kcal/mole refs. -
CH3 (^32) 17, C2H5 (^25) 17,
Q-c#7 22 17,
siH3 (^14 )
BH3 (^18) 6,14 (see tables I and ITI) B2H5 (^48) B2H4 (^89)
‘2H3 , 130 B2H2 (^171)
134%o 19 B4% 60 B5H8 (^56)
%@13 (^67) Y
B(CH3}2CH2 (^19) 6,21 (see tables I and ~1) B(CH3)2 (^28) B(CH3)2H (^) - B(CH3)(CH2)H 33 B(CH3) (^85) B(CH3]H2 (^2) B(CH2)H2 (^50) ;
B5H&H2 (^49) 6,21 (see tables I and III)
‘l@13cH2 60 6,21 (see tables I and III)
