TAP CHI HOA HQC T.50(6) 711-716 THANG 12 NAM 2012
NGHIEN CLfU U THUYET SU" TAO S A N P H A M NU'aC (H2O) HOAC HIDRO NGUYEN Tif (H) TU" P H A N U'NG
CCiA AXIT FULMINIC VOI G 6 C NHJ ( H C N O + NH2)
Nguyen Tr^ng NghTa', Pham Van Ticn'*, Nguyen Thi Minh Hue^
' Vien KT thudt Hda hgc. Trudng Dgi hgc Bdch khoa Hd Ngi
^Khga Hda hgc vd Trung tdm Khoa hgc Tinh todn, Trudng Dgi hgc Suphgm Hd Ngi Den Tda sogn 11-5-2012
Abstract
The mechanism of the reaction between the NH; radical and fulminic acid (HCNO) lo gain H2O or H is studied using computational quantum method, namely DFT (Density Functional Theory), the detail is B3LYP/6- 3I1++G(3df,2p). The potential energy surface (PES) indccated that there are five different reaction pathways which have been carried out. Il shown thai P4 (NCllN+H^O), P3 (HjO+HNCN) are the most favorable. The study also clarified more about the reaction mechanism of the NH; radical with fulminic acid and in fact this reaction is one of the important ones in the atmosphere and combustion chemistry
Keywords: The reaction mechanism of NH; with HCNO, DFT, PES.
1. MO DAU
Axit fulminic (HCNO) la mdt chat trung gian quan trpng trong qua trinh ddt chay lai NO cho viec giam bdt sy d nhiem NO^^ gay ra bdi sy ddt nhien lieu hda thach. Nd duac hinh thanh theo phan img [1-2]:
C H j + N O ^ H C N O + H hoac O + C2H2 -^ HCCO + H;
HCCC + NO ~* HCNO + CO.
HCNO cdn cd the dugc tdng hgp nhd phan ung nhiet phan trong chan khdng 3-phenyl-4- oximinoisoxazol-5(4H). Gan day, ngudi ta da ghi dugc tin hieu axit fulminic trong cac dam may den nhd kinh thien van IRAM 30 m [2]. Hien nay tren thi gidi, phan ung cua HCNO dang dugc quan tam nghien Cliu ca v6 iy thuySt va thyc nghiem nhu phan iirng vdi OH, O, CN,... [2-12]. Gdc amino (NH2) cung la mpt cau tiir trung gian quan trpng trong qua trinh ddt chay hgp chat chua nito theo phan irng:
hogc NH3- NH3
OH HO-3
>NH2+H20 NH2 + OH.
Ngudi ta da do dugc tin hi^u ciia NH2 bang phd hSp thy laser (16.739,90 cm"') [12]. Ngoai ra, da cd nhilu nghien cdu thyc nghiem va ly thuyet ve NH2 nhu phan ling vdi NO, C2H2,... [12, 13].
Trong bai bao nay, trinh bay nghien cuu li thuyit phan umg ciia axit fulminic vdi gdc amino tgo thanh san pham nudc va hidro nguyen td.
2, PHUONG PHAP NGHIEN CUlI
De tinh toan, xay dyng be mat the nang (PES) cho phan ung chiing toi su dung phan mem Gaussian 2003 [15]. Tham sd hinh hpc cac cau true dugc tdi uu hda bang phuang phap phiem ham mat dd B3LYP vi phuong phap nay giiip giam dugc do nhieu spin [16-19], ddng thdi siir dung bp ham co sd Idn la 6-311 ++G(3df,2p). Be mat the nang ciia phan irng dugc thiet lap dya tren tat ca cac cau triic thu dugc va ciing qua ket qua tinh loan chung tdi xac dinh dugc cac gia trj A/Z^ggnu' ^^[
ddi vdi mdi dudng phan irng.
29&.pi , A5; 298.pu
3. KET QUA VA THAO LUAN
Ket qua nghien ciru da dua ra sa dd tgo ra HiO va H tir phan irng HCNO+NH?.
Tren sa dd va be mat the nang, chat phan urng (HCNO, NH2) dugc ki hieu la RA, chat trung gian dugc ki hi?u la li (H, 12, ..., 110), cac trang thai chuyen tiep dugc ki hi^u la Tx/y (TO/I, T1/P2, ...), cac san pham dugc ki hieu la Pi (PI, P2,...).
Trudc tien, ta khao sat phan ung ciia gdc NH2 vdi HCNO. N trong gdc NH2 cd mpt electron ty do tan cdng lan lugt vao cac vj tri H, C, N va O trong phan tu HCNO. Khi gdc NH2 tan cdng vao H hinh thanh trgng thai chuyen tiep TO/H cd tan so ao duy nhat (i = -1455 cm"') irng vdi sy chuyen nguyen tir H tir HCNO sang gdc NHj. Lien kdt H-C trong HCNO
TCHH.T. 50(6), 2012
dugc keo dai tir 1.060 A thanh 1.260 A trong TO/H, dp dai giua nguyen tir H nay vdi N trong NH2 la 1.313 A phii hgp vdi dp dai ciia trgng thai chuyen tiep irng vdi sy chuyen H tir C sang N. Nang lugng cua TO/H cung cao han HCNO+NH2 (RA) phii hgp vdi trgng thai chuyen tilp. Khi N tan cdng vao N trong HCNO, hinh thanh trgng thai chuyen tiep TO/la cd tan sd ao duy nhat la -599 c m ' ung vdi dao dpng hoa trj lien ket N-N hinh thanh san pham trung gian la. Dp dai lien ket giDa hai nguyen tu N la 1,827A phii hgp vdi dp dai lien ket N-N trong trgng thai chuyen tiep. Cau Iriic phan tir HCNO cung thay ddi, goc ZHCN g\am tu 180" xuong 132,6", gdc ZCNO tir 180° xudng 143,5" phii hgp vdi sy hinh thanh trgng thai chuyen liep. Nang lugng ciia TO/la cao han so vdi RA phii hgp vdi trgng thai chuyen liep. Tuy nhien, do 2 nguyen tu N cd dp am di9n Idn va N trong HCNO da bao hda hda tn nen vi?c tgo thanh lien ket N-N d day khdng thugn lgi, trgng thai chuyen tiep (TO/la) va san pham trung gian (la) tgo thanh co nang lugng idn (lan lugt la +27,96 va + 19,34 kcal/mol). Phan ung se rat khd khan khi di
Phgm Van Tien vd cgng stf theo hudng ndy. Khi N tan cong vao nguyen tii 0 ciia HCNO tgo thanh trgng thai chuyen tiep TO/Ib ci5 tan so ao duy nhat -676cm"' ung vdi sy hinh thinh lien ket N-O. Cac dg dai, gdc va nang lugng lien ket deu phii hgp vdi trgng thai chuyen tiep. 6 day, N va O deu cd dg am di^n Idn, sy tgo lien ket khdng thu^
lgi, trgng thai chuyen tiep (TO/Ib) va san pham tmng gian (lb) tgo thanh cd nang lugng ldn (lan lugt la +26,42 va +19,86 kcal/mol). Phan ung se khdng mi ticn di theo hudng nay. Cuoi ciing, N trong NH2 tan cdng vao C trong HCNO tgo thanh san pham trung gian 11 thdng qua trgng thai chuyen tilp TO/1. TO/I cd tan so ao quy nhat -186cm'' irng vdi sy tgo thanh lien ket C-N, cac dg dai Hen ket, gdc va nSng lugng lien kcl deu phii hgp vdi trgng thai chuyen tiep.
Nguyen tu C chua bao hda hda Irj nen vi?c tgo thanh san pham trung gian II thdng qua TO/1 tuong doi thugn Igi, hang rao nang lupng thap (nang lugng tuong quan la l,l9kcal/mol) (hinh 2). Nhu vgy, khi goc NH2 tac dyng vdi HCNO se uu tien theo hudng RA ^ TO/1 (1,19 kcal/mol) ^ 11 (-43,69 kcal/mol)
TO/1
T1/4
IS9 -
T1/2 T2/3 IS1 *- [S2 «- IS3
T5/10
1S10- I
T3/7
^ ^ IS4 - » HN=C=NOH+H (Pi)
T5/P3
^ IS6
HNCN+H2O (P3) NCHN+H2O (P4) HN=C=NOH+H (P1) HONHCN+H (P5) HN 0
I I +H (P2)
=N Hinh I. SCT do phan img cua HCNO+NH, t?o thanh H;0 hojc H
Tucmg tir, tu II ta cung khao sat cac kha nang phan cat lien ket, chuyen vj cac nguyen tir, nhom nguyen tu sau do loai bo cac hudng co nang lui?ng cao ta CO scr do phan ung (hinh 1) va be mgt the nang (hinh 4). Be mat the nang cho thay c6 5 dudng phan iing tao thanh san phSm PI+5, trong dd dudng tao thanh P4 co nang lir(?ng thap nhat.
De tao thanh P4, cd nhieu kha nang xay ra:
Nguyen tu H trong nhdm NH; cua II(-43,69 kcal/mol) chuyen vi sang O qua Tl/5 (-35,48 kcal/mol) thanh 15 (-41,92 kcal/mol). Sau dd Nguyen tii H cdn lai trong nhdm NH ciia 15 tach cung nhdm OH tao thanh P4 (NCHN + H2O: -19,34 kcal/mol) qua hang rao nang lirgng T5P4 (13,45 kcal/mol). Ngoai ra, nguyen tit H trong nhdm NH2 ciia II cd the chuy6n vi sang N qua Tl/7 (-10,20
kcal/mol) thanh 17 (^7,12 kcal/mol). Sau do, nguyen tii H nay chuyen vj sang O d ben qua T7/5 (5,05 kcal/mol) thanh 15 rdi t?o thanh P4. HoSc tir II thanh 17, sau dd H con l?i trong NH chuyen vj sang nguyen tit O qua T7/6 (-7,9 kcal/mol) thanh 16 (-24,34 kcal/mol). Sau dd, H trong 16 chuySn vj 14 Nil sang N dau mjch qua T5/6 (5,35 kcal/mol) thanh 15 rdi cjt thanh 14. ... Cac kha nang nay d^"
cd nang lugng khong cao nen d6u cd kha nang xay ra. Trong do, hudng cd nang lir(?ng thap nhat la:
RA > 11 > 15 > P4(NCHN-t^H20).
Tircmg t\r, ta cd cac dudng t?o cac san pham la:
11 > 17 > 18 > P2(HCNHONH_vong+H) 1 11 > 14 > P1 (NHCNOH-^H)
TCHH, T. 50(6), 2012
n >I5 > P3(NHCN-fH20);
11- » I 7 - >I6 >P5(H0NHCN-fH) Bieu dang luu y la P2 (HCNHONHvdng) la h?
lien hiyp vdng 4 canh vi C lien ket doi vdi N, cdn O va NH van cdn cac cgp e chua sir dgng tao ra he lien hiTp. Lien ket CH-NH cd s^r rut ngan so vdi lien ket
Nghien cuu ly Iht/yel su Igo...
don chiing td cd mpt phSn lien ket ddi. Tuy nhien do la vdng 4 c^nh, siic cang vdng Idn, han nua do cac nguyen tii N va O deu cd dp am dien Idn lam he kem ben, do dai lien ket N-0 ldn hon lien ket don thdng thuang. Vi v?y, P2 va vdng 18 cung nhu T7/8, T8P2 deu cd nang lupng cao, nen dudng nay rat khd cd kha nang xay ra. Cau true chi tiet ciia cac cau tu d hinh 3, n5ng lupng cac cau tir d bang 2.
1 060 J-155J.200 179.9 1.02I©J.027
RA (0,00)
1 260J.313
173Ai2) - ^ 'T'.iso \
TO/H (5,36)
1.827 132.6 „ 1 203
TO/la (27,96)
TO/1 (1,19) 11 (-43,69) la (19,34) lb (19,86)
Hinh 2- Hinh hpc cua cic trang thai chuyen liep, san pham trung gian khi NH2 t5n cong vao H, C, N, O trong phan tu HCNO. (Dau cham (.) thay cho dau phay (,) trong phan thap phan. Gig trj trong ngoac la nang lugng tuong quan cua
cau tii tuong ung, don vj kcal/mol. Do dai lien kel tinh theo Angstrom (A), goc lien k6t tinh iheo dp (")) Bang 1 cho thiy dudng tgo P4 (H2O + NCHN)
CO bien thien the dang nhiet-dang ap AG29g« 0 nen phan ling thugn lgi ve mat nhiet dpng, hon nua bien thien entropi AS^gg kha ldn cd the dy doan phan ling thugn Igi ban khi d nhiet dp cao. Be mat the nang cho thay dudng nay cd hang rao nang lugng tuang ddi thap so vdi cac dudng khac. Vi vgy cd the dy doan dudng nay ddng gdp chii yeu vao san pham phan ling, nhat la khi d nhiet do cao. Dudng phan ling tgo thanh P3 (H2O+NHCN) thugn Igi hon so vdi dudng P4 ve mgt nhipt dgng, nhung hang rao nang lugng cao hon mdt chut, do dd cd the dy doan dudng P3 cd ddng gdp vao san pham, sy ddng gdp
nay tang len khi phan iing d nhiet dp cao. Dudng tao PI (NHCNOH+H), P5 (HONHCN+H) cd AGj^g duang nen khdng cd kha nang xay ra d 298 K, nhung A^jgg duong nen khi phan iing d nhiet dp cao cd the xay ra, tuy nhien khi dd cung chi ddng gdp rat ft vi hang rao nang lugng cao. Dudng tao P2 (CHNHON(vong) + H) vdng 4 canh, lgi cd N, O dp am dien Idn nen kem ben cd AG^gg» 0, AS2gg< 0, han nira hang rao nang lugng rat Idn nen khdng the di theo hudng nay. Tir nhdng phan tich d tren cd the thay xet ve mat nhiet dpng hpc thu ty uu tien ciia cac dudng phan iing nhu sau; P4, P3 > P5, PI > P2. B^
mat the nang cua cac dudng phan iing d hinh 4.
Bang 1: AH,., AG
Phan ling
HCNO+NH2 -> NHCNOH-fH CHNHON(vdng)+H
H2O+NHCN HjO+NCHN HONHCN+H
pu, ASpu cua cac dudng phan img Ky hieu san
pham PI P2 P3 P4 P5
AS, cal/mol.K
0,8 -3,2 11,3 11,8 0,9
AH, kcal/mol
10,3 50,8 -63,6 -19,7 9,5
AG, kcal/mol
10,0 51,7 -66,9 -23,1 9,3
T C H H , T. 50(6), 2 0 1 2
Hinh 3. Hinh hpc mpt so cau lit trong s a d o phan irng H C N O + N H i tjio t h a n h H2O va H. (DSu chjm (.) thay cho dau phay trong p h i n thap phan. D p dai lien kel tinh t h e o A n g s t r o m ( A ) , gdc lien ket tinh theo dp (°))
Bang 2: Nang lupng mpt sd cau t u trong s o d o phan img Tieu
phan 11 12 13 14
EzpE, Hartree/hat
0,0492068 0,0495460 0,0483537 0,0484827
Eo + EzpE,
-224,57834 -224,55512 -224,52018 -224,54980
AE,
-43,69 -29,10 -7,16 -25,76
T i e u p h a n Tl/S Tl/7 Tl/4 T2/3
H C N O + N H j t j o thanh H2O va H EzpE.
0 , 0 4 5 5 5 2 5 0 , 0 4 3 7 5 9 4 0 , 0 4 4 5 5 3 9 0,0440166
Eo + EzpE,
-224,56527 -224,52502 -224,51264 - 2 2 4 , 4 7 9 3 2
/iE, kcal/mol
-35,48 -10,20
_^y2__
18,51
714
TCHH, T. 50(6), 2012 Nghien cihi ly thuyet su tgo...
Tieu phan IS 16 17 18 19 110 TO/1 Tl/2
EZPE, Hartree/h^t 0,0492077 0,0487396 0,0496685 0,0493802 0,0490729 0,0482769 0,0419352 0,0484998
EO -f EZPE, Hartree/hat -224,57552 -224,54754 -224,58380 -224,46094 -224,54034 -224,54500 -224,50689 -224,54491
AE, kcal/mol
-41,92 -24,34 -47,12 30,05 -19,82 -22,75 1,19 -22,69
Tieu phan T3/7 T4/P1 TS/P3 TS/P4 TS/Pl TS/7 TS/6 T6/7
EZPE, Hartree/hgt 0,0470206 0,0390183 0,0408390 0,0439824 0,0390355 0,0429005 0,0436047 0,0434464
EO + EZPE, Hartree/hat -224,50515 -224,48712 -224,47930 -224,48737 -224,48608 -224,50074 -224,50026 -224,52137
AE, kcal/mol
2,28 13,61 18,52 13,45 14,26 5,05 5,35 -7,90 Tir cac thdng so nhi^t d$ng va nang lugng phan tu cua cac chat phan ung va cac san pham phan iing se xac djnh dugc cac gia trj A/Zj, , AG' , ASjqg .„ doi vdi mdi dudng phan iing.
Hinh 4. Be m|t thS nang phan ling HCNO + NHj tao thanh H2O va H. (DSu chim (.) thay cho dau phay trong phin thap phan Dp dai lien k6t tinh theo Angstrom (A), gdc lien kSt tinh theo dp (°)) 4. KET LUAN
Da thia Ijp dupc bS m|t thj nang, giai thich ca che phan iing HCNO+NH2 tao thanh H2O va H.
Thdng qua dd dua ra dupc cac tham sd cau true hinh hpc, tan sd dao dpng cho mdi cau tir. Tir PES thu dupc chung tdi dy doan: Trong cac phan iing tao thanh H2O va H tir phan iing HCNO+NH2, dudng phan ling P2 (CHNHON(vdng)+H) khdng tham gia vao san pham; dudng phan iing P4 (H20-t-NCHN), P3 (H2O+NHCN) chiem uu the nhat va duang phan
ung PI (NHCNOH+H), P5 (HONHCN+H) cung cd the ddng gdp mpt phan neu phan irng d nhiet dp cao.
Ngoai ra citng da tinh dupc cac gia trj
^m.p.' ^G°„p„ AS'^„j„ cho tat ca cac dudng phan img.
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T C H H , T. 50(6), 2 0 1 2
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Lien h4: P h a m V a n T i e n
Trucrng Dgi hpc Bach K h o a Ha N g i
So 1 Dgi C 6 Vi?t, Hai Ba Trung, Ha N g i , Viet N a m Email: [email protected]
Dien thogi; 0 9 1 7 8 8 8 5 5 3 .
