Objectives Bromination and bromoalkylation reactions of CNT are very promising pathways to grafting of electrophilic sites. However, only sparse experimental data is available in the literature. The present work is a broad and systematic study to optimize the bromination and bromoalkylation yield of multi-walled CNT (Baytubes® C150P) using Lewis acids as catalysts. Bromination and bromoalkylation of multi-walled CNT were investigated by systematic variation of processing parameters. Eight different reaction times, three reaction temperatures, nine solvents, twelve catalysts and eleven electrophile reagents were studied with respect to bromination yield. Also the substitutability of the introduced bromine was studied. For this, the reaction of brominated CNT with 4-(trifluoromethyl)benzyl mercaptane was investigated. The substitution efficiency of bromine by this fluorinated compound was quantified by XPS analysis. The optimum bromimation procedure will be used to study the coupling of specifically-synthesized mercaptanes with brominated or bromoalkylated nanotubes. HH H H H H H H H H HH H H H H Br Br Br Br Br H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H Br Br Br Br Br Br Br Br Br Br Br Br Br Br Studied reaction parameters • Solvents: DCM, Et 2 O, iPr 2 O, nBu 2 O, n-C 6 H 14 , n-C 9 H 20 , n-C 12 H 26 , Diglyme, Triglyme, MeCN/Dioxane, 1,2-Dichlorobenzene, Bromoforme, Ethylendibromide, H 2 O/Dioxane • Lewis/Brönstedt-Acids: BF 3 •Et 2 O, BBr 3 , AlBr 3 , FeBr 3 , SiBr 4 , SnBr 4 , VBr 3 •Diglyme, ZnBr 2 • (THF) 2 , TiBr 4 , DBPO, MsOH, H 3 PO 4 • Reaction Temperatures: RT, 50 ºC, 95 ºC, 200 ºC • Durations: 1h, 3h, 4h, 5h, 1d, 3d, 1 Wo, 2 Wo • Reagents for bromination/alkylation: Br 2 , 1,6-Dibromohexane, p-Xylylendibromide, SOCl 2 , SOBr 2 , SO 2 Cl 2 , Allylbromide, trans-1,4-Dibromo-2-Butene, 4-Methylbenzylbromide, 6-Bromo-1-Hexanole, 4-Chloromethylbenzylalcohol, 5-Bromo-1-Pentene BF3 BBr3 AlBr3 FeBr3 ZnBr2 TiBr4 SiBr4 SnBr4 Et2O n-C6H14 CH2Cl2 iPr2O 0 0,5 1 1,5 2 2,5 3 XPS at% Br Lewis acid Solvent Baytubes bromination Et2O n-C6H14 CH2Cl2 iPr2O BF3 BBr3 AlBr3 FeBr3 ZnBr2 TiBr4 SiBr4 SnBr4 Et2O n-C6H14 CH2Cl2 iPr2O 0 0,5 1 1,5 2 2,5 3 XPS at% Br Lewis acid Solvent Baytubes bromohexylation with 1,6-Dibromohexane Et2O n-C6H14 CH2Cl2 iPr2O BF3 BBr3 AlBr3 FeBr3 ZnBr2 TiBr4 SiBr4 SnBr4 Et2O n-C6H14 CH2Cl2 iPr2O 0 0,5 1 1,5 2 2,5 3 XPS at% Br Lewis acid Solvent Baytubes 4-Bromomethylbenzylation Et2O n-C6H14 CH2Cl2 iPr2O High temperature bromination at 200 deg. Celsius 0 5 10 15 20 25 SnBr4 n- Dodecane AlBr3 Di-n- Hexylether AlBr3 Triglyme AlBr3 n- Dodecane FeBr3 Di-n- Hexylether SiBr4 n- Dodecane ZnBr2 Triglyme TiBr4 Diglyme VBr3 Diglyme Br2 in n- Dodecane Reaction parameters for 2,5h at.% Br at%Br Observed general trends • Bromination is more effective than bromoalkylation • The Lewis acids AlBr 3 ,FeBr 3 ,SnBr 4 are most reactive in this order • In contrast to bromination bromoalkylation leads to 100% substitutable bromine at least at 90°C or below • In low-temperature reactions unpolar solvents are superior to ethers • In high-temperature bromination di-n-Hexylether (though expensive) is superior to dimethylethers of glycols and alkanes • High-temperature bromination leads to about ten times as much bromine than low-temperature bromination including intercalated bromine • Further and concluding experiments are in progress Substitution with 4-Trifluoromethylbenzylmercaptane 0 0,5 1 1,5 2 2,5 Bromine AlBr3 DCM 4,5h RT p-Xylylenedibromide SnBr4 1h 95 deg n-Nonane 1,6-Dibromohexane 5h 95 deg SnBr4 n-Nonane non-brominated Baytubes Pretreatment before substitution at.% F or at.% Br XPS at%Br before deriv. at%F after deriv. at%Br after deriv. Conclusions Optimization of bromination or bromoalkylation may be necessary for each type of CNT material due to individual reactivity. For Baytubes, this reaction is efficiently catalyzed by AlBr 3 either in DCM at lower temperature or in di-n-Hexylether at 200 °C. Bromoalkylation leads to 100% substitutable bromine but at a lower bromine concentration. The problem of intercalated bromine, which would not be substitutable, remains to be solved if Br 2 is used. Systematic study of Lewis acid-catalyzed bromination and bromoalkylation of multi-walled carbon nanotubes S. Hanelt, Jörg F. Friedrich, A. Meyer-Plath BAM – Bundesanstalt für Materialforschung und –prüfung, Unter den Eichen 87, 12205 Berlin, Germany
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
-
ObjectivesBromination and bromoalkylation reactions of CNT are very promising pathways to grafting of electrophilic sites. However, only sparse experimental data is available in the literature. The present work is a broad and systematic study to optimize the bromination and bromoalkylation yield of multi-walled CNT (Baytubes® C150P) using Lewis acids as catalysts. Bromination and bromoalkylation of multi-walled CNT were investigated by systematic variation of processing parameters. Eight different reaction times, three reaction temperatures, nine solvents, twelve catalysts and eleven electrophile reagents were studied with respect to bromination yield. Also the substitutability of the introduced bromine was studied. For this, the reaction of brominated CNT with 4-(trifluoromethyl)benzyl mercaptanewas investigated. The substitution efficiency of bromine by this fluorinated compound was quantified by XPS analysis. The optimum bromimation procedure will be used to study thecoupling of specifically-synthesized mercaptanes with brominated or bromoalkylatednanotubes.
HH
HH
H
H
H
H
HH
HH
H
H
H
H
Br
Br
Br
Br
BrH
H
H
H
H
HHH
HH
HHH
HH
H
H
H
H
HH
HH H
HH
H HH
H
H
H
H
H
H
HH
HH
H
H
H
H
H
H
H
H
H
H
HH
HH
H
H
H
H
HH
HH
BrBrBrBr
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Studied reaction parameters• Solvents: DCM, Et2O, iPr2O, nBu2O, n-C6H14 , n-C9H20 , n-C12H26 , Diglyme, Triglyme,
MeCN/Dioxane, 1,2-Dichlorobenzene, Bromoforme, Ethylendibromide,H2O/Dioxane
• Lewis/Brönstedt-Acids: BF3•Et2O, BBr3, AlBr3, FeBr3, SiBr4, SnBr4, VBr3•Diglyme, ZnBr2• (THF)2, TiBr4, DBPO, MsOH, H3PO4
• Reaction Temperatures: RT, 50 ºC, 95 ºC, 200 ºC• Durations: 1h, 3h, 4h, 5h, 1d, 3d, 1 Wo, 2 Wo• Reagents for bromination/alkylation: Br2, 1,6-Dibromohexane, p-Xylylendibromide, SOCl2,
SOBr2, SO2Cl2, Allylbromide, trans-1,4-Dibromo-2-Butene, 4-Methylbenzylbromide, 6-Bromo-1-Hexanole, 4-Chloromethylbenzylalcohol,5-Bromo-1-Pentene
BF3
BB
r3
AlB
r3
FeB
r3
ZnB
r2
TiB
r4
SiB
r4
SnB
r4
Et2On-C6H14
CH2Cl2iPr2O0
0,51
1,52
2,5
3
XPS at% Br
Lewis acid
Solvent
Baytubes bromination
Et2O
n-C6H14CH2Cl2
iPr2O
BF3
BB
r3
AlB
r3
FeB
r3
ZnB
r2
TiB
r4
SiB
r4
SnB
r4
Et2On-C6H14CH2Cl2iPr2O
0
0,5
1
1,5
2
2,5
3
XPS at% Br
Lewis acid
Solvent
Baytubes bromohexylation with 1,6-Dibromohexane
Et2On-C6H14
CH2Cl2
iPr2O
BF3
BBr
3
AlBr
3
FeB
r3
ZnBr
2
TiB
r4
SiB
r4
SnB
r4
Et2On-C6H14CH2Cl2iPr2O
0
0,5
1
1,5
2
2,5
3
XPS at% Br
Lewis acid
Solvent
Baytubes 4-Bromomethylbenzylation
Et2O
n-C6H14CH2Cl2
iPr2O
High temperature bromination at 200 deg. Celsius
0
5
10
15
20
25
SnBr4 n-Dodecane
AlBr3 Di-n-Hexylether
AlBr3Triglyme
AlBr3 n-Dodecane
FeBr3 Di-n-Hexylether
SiBr4 n-Dodecane
ZnBr2Triglyme
TiBr4Diglyme
VBr3Diglyme
Br2 in n-Dodecane
Reaction parameters for 2,5h
at.%
Br
at%Br
Observed general trends• Bromination is more effective than bromoalkylation• The Lewis acids AlBr3,FeBr3,SnBr4 are most reactive in this order• In contrast to bromination bromoalkylation leads to 100% substitutable bromine at least at
90°C or below• In low-temperature reactions unpolar solvents are superior to ethers• In high-temperature bromination di-n-Hexylether (though expensive) is superior to
dimethylethers of glycols and alkanes• High-temperature bromination leads to about ten times as much bromine
than low-temperature bromination including intercalated bromine• Further and concluding experiments are in progress
Substitution with 4-Trifluoromethylbenzylmercaptane
0
0,5
1
1,5
2
2,5
Bromine AlBr3 DCM 4,5h RT p-Xylylenedibromide SnBr4 1h 95deg n-Nonane
1,6-Dibromohexane 5h 95 degSnBr4 n-Nonane
non-brominated Baytubes
Pretreatment before substitution
at.%
F o
r at.%
Br X
PS
at%Br before deriv. at%F after deriv. at%Br after deriv.
ConclusionsOptimization of bromination or bromoalkylation may be necessary for each type of CNT material due to individual reactivity. For Baytubes, this reaction is efficiently catalyzed byAlBr3 either in DCM at lower temperature or in di-n-Hexylether at 200 °C. Bromoalkylationleads to 100% substitutable bromine but at a lower bromine concentration. The problem of intercalated bromine, which would not be substitutable, remains to be solved if Br2 is used.
Systematic study of Lewis acid-catalyzed bromination and bromoalkylation of multi-walled carbon nanotubesS. Hanelt, Jörg F. Friedrich, A. Meyer-Plath
BAM – Bundesanstalt für Materialforschung und –prüfung, Unter den Eichen 87, 12205 Berlin, Germany
Related Documents
