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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
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Systematic study of Lewis acid-catalyzed bromination and ......The present work is a broad and systematic study to optimize the bromination and bromoalkylation yield of multi-walled

Jan 31, 2021

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  • 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