Review 6: organic peroxides in radical synthesis ... - Acros Organics
Review 6: organic peroxides in radical synthesis ... - Acros Organics
Review 6: organic peroxides in radical synthesis ... - Acros Organics
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REVIEW 6<br />
Organic Peroxides <strong>in</strong><br />
Radical Synthesis Reactions<br />
Organic Peroxides<br />
Organic Peroxides<br />
New from <strong>Acros</strong> <strong>Organics</strong><br />
J. Meijer, A.H. Hogt and B. Fischer<br />
Akzo Nobel Polymer Chemicals Laboratory Deventer<br />
Zutphenseweg 10, PO Box 10, 7400 AA Deventer, The Netherlands.
Organic Peroxides <strong>in</strong> Radical Synthesis Reactions<br />
J. Meijer, A.H. Hogt and B. Fischer<br />
Akzo Nobel Polymer Chemicals Laboratory Deventer<br />
Zutphenseweg 10, PO Box 10, 7400 AA Deventer, The Netherlands.<br />
Contents<br />
I. Introduction<br />
II. Reactivity of <strong>organic</strong> <strong>peroxides</strong><br />
III. Oxidation reactions with <strong>organic</strong> <strong>peroxides</strong><br />
IV. Radical reactions with <strong>organic</strong> <strong>peroxides</strong><br />
V. Functionalization reactions with <strong>organic</strong> <strong>peroxides</strong><br />
VI. Conclud<strong>in</strong>g remarks<br />
VII. References<br />
VIII. Table of abbreviations<br />
IX. List<strong>in</strong>g of Organic <strong>peroxides</strong> from <strong>Acros</strong> <strong>Organics</strong><br />
1
I. Introduction<br />
Radicals can be used as synthetic <strong>in</strong>termediates <strong>in</strong> reactions which are often difficult<br />
to accomplish by other means and which can selectively occur under very mild conditions.<br />
The protection of functional groups, often essential for synthetic sequences of ionic reactions,<br />
is mostly not required for <strong>radical</strong> reactions [Curran e.a., 1996].<br />
Organic <strong>peroxides</strong> are a very versatile source of <strong>radical</strong>s that are formed after the<br />
thermally <strong>in</strong>duced homolysis of the peroxide bond. The major <strong>radical</strong>-molecule reactions are<br />
additions and SH 2 –reactions, e.g. H-abstraction, atom transfer, unimolecular reactions, e.g.<br />
decarboxylation, β-scission and rearrangements, e.g. 1,5-H-abstraction [Ingold, 1973]. In<br />
<strong>synthesis</strong> reactions, undesired <strong>radical</strong>-<strong>radical</strong> reactions such as <strong>radical</strong> comb<strong>in</strong>ation and<br />
disproportionation can be avoided by proper choice of the type of peroxide and reaction<br />
conditions. Another major application of <strong>organic</strong> <strong>peroxides</strong> <strong>in</strong> syntheses is oxidation, which is<br />
a non-<strong>radical</strong> reaction [Rao and Mohan, 1999].<br />
II.<br />
Reactivity of <strong>organic</strong> <strong>peroxides</strong><br />
Organic <strong>peroxides</strong> can have a variety of characteristics depend<strong>in</strong>g on their chemical<br />
structure and reactivity. The reactivity of the <strong>peroxides</strong> depends on the peroxide group<br />
configuration and on the type of substituents. Organic <strong>peroxides</strong> can be classified <strong>in</strong>to<br />
different groups depend<strong>in</strong>g on their chemical structures (see Fig. 1).<br />
Type of peroxide<br />
Structure<br />
Hydro<strong>peroxides</strong> R O O H<br />
Ketone <strong>peroxides</strong><br />
Peroxyacids<br />
R1<br />
H O O O O H<br />
O<br />
R O O<br />
R2<br />
H<br />
n=1,2<br />
Dialkyl<strong>peroxides</strong> R O O R<br />
Peroxyesters<br />
Peroxycarbonates<br />
Diacyl<strong>peroxides</strong><br />
Peroxydicarbonates<br />
Peroxyketals<br />
Cyclic ketone <strong>peroxides</strong><br />
O<br />
R1 O O<br />
Figure 1. Types of <strong>peroxides</strong> and general chemical structures.<br />
R1<br />
R<br />
O<br />
O<br />
O<br />
O<br />
O<br />
O<br />
O<br />
O<br />
R2<br />
O<br />
R<br />
R2<br />
O<br />
R O O O O R<br />
R1<br />
R O O O O R<br />
R1<br />
R2<br />
O<br />
R2<br />
O<br />
n=2,3<br />
2
The thermally <strong>in</strong>duced homolysis of the peroxidic bonds yield oxy-<strong>radical</strong>s. The<br />
decomposition rate of <strong>peroxides</strong> does not only depend on the class of peroxide but on the<br />
type of R-group as well. The reactivity and the sensitivity of the <strong>peroxides</strong> to <strong>radical</strong> attack<br />
(<strong>in</strong>duced decomposition) is strongly related to its structure. Therefore, <strong>organic</strong> <strong>peroxides</strong> are<br />
<strong>radical</strong> <strong>in</strong>itiators with a very broad range of reactivities [Akzo Nobel PC product catalogue].<br />
This is illustrated <strong>in</strong> Figure 2, which shows the half-life time (t_) of a number of <strong>peroxides</strong><br />
aga<strong>in</strong>st temperature.<br />
10<br />
EHP<br />
TBPB<br />
Half life time (h)<br />
1<br />
TBPP<br />
LPO<br />
DTBP<br />
TBHP<br />
BPO<br />
0,1<br />
0 50 100 150 200 250<br />
Temperature (°C)<br />
Figure 2. Half-life times of various <strong>organic</strong> <strong>peroxides</strong> as function of temperature (see: Abbreviations).<br />
The thermal decomposition of <strong>organic</strong> <strong>peroxides</strong> is a first order reaction. Increase <strong>in</strong><br />
temperature of about 10°C results <strong>in</strong> a 2-3-fold <strong>in</strong>crease <strong>in</strong> decomposition rate. In the case of<br />
peresters and diacyl<strong>peroxides</strong>, the reactivity of <strong>organic</strong> <strong>peroxides</strong> is affected to a high degree<br />
by the type of substituents on the carbon atom adjacent to the peroxy bond. Increas<strong>in</strong>g alkyl<br />
substitution on a given peroxyester shortens the half-life by a factor of more than 60, on<br />
diacyl<strong>peroxides</strong> by a factor of 9000. This substitution effect is much less prom<strong>in</strong>ent for other<br />
<strong>peroxides</strong> such as peroxy (di) carbonates and dialkyl<strong>peroxides</strong> where substituents are varied<br />
on the ß-position to the peroxy group. An extensive review on peroxy compounds is reported<br />
by Sheppard [Sheppard, 1985].<br />
Decomposition rates of <strong>peroxides</strong> are <strong>in</strong> pr<strong>in</strong>ciple depend<strong>in</strong>g on the solvent used,<br />
ma<strong>in</strong>ly due to differences <strong>in</strong> polarity. For example, the one-hour half-life temperature of di-tertbutyl<br />
peroxide (DTBP) <strong>in</strong>creases about 20 degrees chang<strong>in</strong>g from chlorobenzene to an<br />
aliphatic solvent [Akzo Nobel - <strong>in</strong>ternal <strong>in</strong>formation].<br />
The viscosity of the medium can also have an effect on the rate of peroxide decomposition<br />
[Lazar, 1983; Van Drumpt and Oosterwijk, 1976].<br />
III.<br />
Oxidation reactions with <strong>organic</strong> <strong>peroxides</strong><br />
Peroxyacids are mostly used for the epoxidation of unsaturated compounds. Most<br />
important are the Baeyer-Villiger reaction of carbonyl compounds, oxidation of nitrogen and<br />
sulfur compounds (see Fig. 3) [Rao and Mohan, 1999]. It is generally accepted that such<br />
oxidations are non-<strong>radical</strong> reactions.<br />
3
R 3 N(O)<br />
R 3 N<br />
O<br />
EPOXIDATION<br />
O<br />
R O O H<br />
PEROXY ACID<br />
R 2 S<br />
R 2 S(O) n=1,2<br />
R 1 C(O)R 2<br />
R 1 C(O)OR 2<br />
BAEYER-VILLIGER<br />
Figure 3. Oxidation via peroxy-compounds.<br />
IV.<br />
Radical reactions with <strong>organic</strong> <strong>peroxides</strong><br />
Through homolytic scission <strong>organic</strong> <strong>peroxides</strong> primarily generate oxy-<strong>radical</strong>s: alkoxy-<br />
, acyloxy- and/or oxycarbonyloxy-<strong>radical</strong>s [Kochi, 1973 -a].<br />
Oxy-<strong>radical</strong>s can also be generated from peroxyesters, diacyl<strong>peroxides</strong> and hydro<strong>peroxides</strong><br />
by redox systems [ Kochi, 1973 -b]. (see Fig. 4).<br />
O<br />
*<br />
O<br />
*<br />
DTAP<br />
DCP<br />
O<br />
DTBP<br />
BPO<br />
O *<br />
O *<br />
R 1 OOR 2<br />
O<br />
O<br />
CPDC<br />
BPIC<br />
C 16 H 33 O O * O O *<br />
H<br />
MPDC<br />
TBCPDC<br />
C 14 H 29<br />
O<br />
O<br />
O *<br />
O<br />
O<br />
*<br />
O<br />
Figure 4. Generation of oxy-<strong>radical</strong>s via peroxy-compounds.<br />
4
An important reaction of alkoxy-<strong>radical</strong>s is β-scission, and of acyloxy-<strong>radical</strong>s<br />
decarboxylation, both reactions result<strong>in</strong>g <strong>in</strong> the formation of carbon-<strong>radical</strong>s. In contrast,<br />
alkoxycarbonyloxy-<strong>radical</strong>s do not show decarboxylation [Kochi, 1973-a]. (see Fig. 5).<br />
C 2 H 5<br />
DTAP<br />
DTBP<br />
CH 3 *<br />
*<br />
*<br />
H<br />
TBPIB<br />
TBPP<br />
*<br />
R 1 OOR 2<br />
BPO<br />
TBPEH<br />
* *<br />
LPO<br />
BTMHP<br />
C 11 H 23 *<br />
*<br />
Figure 5. Generation of carbon-<strong>radical</strong>s via peroxy-compounds.<br />
In the presence of a substrate, oxy-<strong>radical</strong>s (R-H) generate substrate-<strong>radical</strong>s which<br />
may undergo comb<strong>in</strong>ation reactions, addition reactions to unsaturated compounds or atomtransfer<br />
reactions. Examples of such reactions <strong>in</strong> practical applications are (see Fig. 6):<br />
comb<strong>in</strong>ation of phenylisopropyl-<strong>radical</strong>s to 2,3-dimethyl-2,3-diphenylbutane, applied as flameretardant<br />
synergist [Regitz and Giese, 1989 -a], addition of methylphosphorous monoisobutyl<br />
ester to v<strong>in</strong>ylacetic acid ethylester, used <strong>in</strong> the <strong>synthesis</strong> of the glufos<strong>in</strong>ate herbicide<br />
[Meiji Seika Kaisha, 1982], and atom transfer of brom<strong>in</strong>e to a substituted tolyl-<strong>radical</strong>, yield<strong>in</strong>g<br />
a flame retardant [Tosoh, 1999]. In addition, oxy-<strong>radical</strong>s can be used for the racemization of<br />
optically active chrysanthemic acid or its ester used for the <strong>synthesis</strong> of pyrethr<strong>in</strong>e<br />
<strong>in</strong>secticides [Sumitomo, 1992].<br />
5
R 1 OOR 2<br />
R 1 O * * OR 2<br />
R-H<br />
ABSTRACTION<br />
R 1 OH + HOR<br />
2x<br />
2<br />
X-Y<br />
R-R R*<br />
R-X + Y *<br />
COMBINATION<br />
ATOM TRANSFER<br />
H<br />
Br<br />
R<br />
H<br />
X<br />
H<br />
[Regitz and Giese, 1989-a]<br />
ADDITION<br />
[Tosoh, 1999]<br />
O<br />
O<br />
P<br />
O<br />
O<br />
[Meiji Saika Kaisha, 1982]<br />
Figure 6. Reactions of oxy-<strong>radical</strong>s with substrates R-H.<br />
Oxy-<strong>radical</strong>s can add to unsaturated compounds. They may also undergo competitive<br />
reactions such as β-scission <strong>in</strong> case of alkoxy-<strong>radical</strong>s, and decarboxylation <strong>in</strong> case of<br />
acyloxy-<strong>radical</strong>s. The formed carbon-<strong>radical</strong>s will <strong>in</strong> most cases also add to the unsaturated<br />
compounds [Kochi, 1973-Oxy-<strong>radical</strong>s; Regitz and Giese, 1989 -b].<br />
6
V. Functionalization reactions with <strong>organic</strong> <strong>peroxides</strong><br />
Some <strong>organic</strong> <strong>peroxides</strong> with particular structures have a specific performance <strong>in</strong><br />
functionalization reactions. Examples are <strong>peroxides</strong> with unsaturated groups, hydroxyl groups<br />
and acid groups and multi-functional <strong>peroxides</strong> with unsaturated and acid groups (see Fig. 7).<br />
Peroxide CAS nr. Structure<br />
tert-butyl-1,1-dimethylpropenyl<br />
peroxide<br />
114041-94-0<br />
O<br />
O<br />
tert-butylperoxy<br />
allylcarbonate<br />
65700-08-5<br />
O<br />
O<br />
O<br />
O<br />
tert-butylperoxy-6-<br />
hydroxyhexanoate<br />
(not yet<br />
assigned) O O<br />
O<br />
O<br />
H<br />
tert-butylperoxy-3-<br />
carboxypropanoate<br />
28884-42-6<br />
O<br />
O<br />
O<br />
O<br />
O<br />
H<br />
tert-butylmonoperoxymaleate<br />
1931-62-0<br />
O<br />
O<br />
O<br />
O<br />
O<br />
H<br />
Figure 7. Functional <strong>peroxides</strong>.<br />
With particular unsaturated <strong>peroxides</strong>, functional groups can be <strong>in</strong>corporated <strong>in</strong> a<br />
substrate after an <strong>in</strong>duced decomposition reaction and subsequent rearrangement (see Fig.<br />
8). Epoxide groups have been <strong>in</strong>troduced <strong>in</strong> various substrates such as cyclohexane, furan,<br />
methylproprionate, acetonitrile and dichoromethane, by allylic <strong>peroxides</strong>, e.g. t-butyl-1,1-<br />
dimethyl-propenyl peroxide [Montaudon e.a., 1987]. Crown ethers have been functionalized<br />
with cyclic carbonate groups us<strong>in</strong>g t-butylperoxy allylcarbonate [Maillard e.a., 1989].<br />
R-H<br />
+ O<br />
* R * +<br />
O H<br />
R *<br />
O<br />
O<br />
R<br />
O<br />
*<br />
O<br />
R * +<br />
O<br />
R<br />
O<br />
O O O<br />
++<br />
O O<br />
Figure 8. Functionalization via unsaturated peroxy-compounds.<br />
O<br />
*<br />
Tert-butylmonoperoxymaleate and t-butylperoxy-3-carboxypropanoate are capable of<br />
<strong>in</strong>corporat<strong>in</strong>g acid and/or anhydride groups <strong>in</strong> substrates, probably via H-abstraction and an<br />
addition or comb<strong>in</strong>ation reaction [Mann<strong>in</strong>g and Moore, 1997]. Primary hydroxyl functions can<br />
be <strong>in</strong>troduced us<strong>in</strong>g t-butylperoxy-6-hydroxyhexanoate via a decarboxylation and addition<br />
reaction to unsaturated substrates [ Akzo Nobel, 2001].<br />
7
VI.<br />
Conclud<strong>in</strong>g remarks<br />
There are several important parameters for the choice of a peroxide for use <strong>in</strong><br />
chemical syntheses. The physical and chemical stability affects the storage and handl<strong>in</strong>g<br />
properties, the temperature-dependent rate of decomposition determ<strong>in</strong>es the reactivity at the<br />
process conditions. The <strong>radical</strong>s formed after decomposition must be efficient for the desired<br />
<strong>radical</strong> reaction. Peroxides may also be selected for specific rearrangements or specific<br />
coupl<strong>in</strong>g reactions, which can <strong>in</strong>troduce functional groups <strong>in</strong>to substrates. Decomposition<br />
products of the <strong>peroxides</strong> have to be taken <strong>in</strong> account dur<strong>in</strong>g the purification process.<br />
Organic <strong>peroxides</strong> are well established synthetic agents <strong>in</strong> the manufacture of many<br />
pharmaceutical <strong>in</strong>termediates, herbicides, <strong>in</strong>secticides and various other f<strong>in</strong>e chemicals.<br />
Organic <strong>peroxides</strong> offer opportunities to reduce the number of reaction steps <strong>in</strong> synthetic<br />
routes apply<strong>in</strong>g classical synthetic procedures. Moreover, <strong>in</strong>troduction of functional groups<br />
can be achieved by us<strong>in</strong>g special <strong>organic</strong> <strong>peroxides</strong>. In many cases these reactions are<br />
unprecedented <strong>in</strong> non-<strong>radical</strong> chemistry.<br />
Organic <strong>peroxides</strong> comb<strong>in</strong>e a number of <strong>in</strong>terest<strong>in</strong>g features for the application <strong>in</strong> <strong>organic</strong><br />
<strong>synthesis</strong>:<br />
! High purity<br />
! Good solubility on most <strong>organic</strong> systems, enabl<strong>in</strong>g homogeneous reaction conditions<br />
! Well def<strong>in</strong>ed and temperature controlled reactivity<br />
! High efficiency<br />
! Favorable cost/performance ratio<br />
8
VII.<br />
References<br />
Curran, D.P., Porter, N.A., Giese, B., Stereochemistry of Radical Reactions, VCH<br />
Verlagsgesellschaft, We<strong>in</strong>heim, Germany (1996), pp. 1-22.<br />
Rao, A.S. and Mohan, H.R., <strong>in</strong>: Burke, S.D. and Danheiser, R.L., Handbook of Reagents for<br />
Organic Synthesis, Oxidiz<strong>in</strong>g and Reduc<strong>in</strong>g Agents, Wiley, Chichester, UK (1999), pp. 84-89.<br />
Ingold, K.U., Rate constants for free <strong>radical</strong>s <strong>in</strong> solution, <strong>in</strong>: Kochi, J.K. (Ed.), Free Radicals,<br />
Vol. I, Wiley, New York (1973), Chapter 11, pp. 37-112.<br />
Akzo Nobel PC Product Catalogue.<br />
Sheppard, Ch. S., <strong>in</strong>: Mark, H.F., Bikales, N.M., Overberger, C.G. and Menges, G. (Eds.),<br />
Encyclopedia of Polymer Science and Eng<strong>in</strong>eer<strong>in</strong>g, Vol. 11, Wiley, New York (1985), p. 1.<br />
Akzo Nobel, <strong>in</strong>ternal <strong>in</strong>formation.<br />
Lazar, M., <strong>in</strong>: Patai, S (Ed.), The Chemistry of Functional Groups, Peroxides, Wiley, New York<br />
(1983), p. 177.<br />
Van Drumpt, J.D. and Oosterwijk, H.H.J., J. Polym. Sci., Polym. Chem. Ed., 14 (1976), 1495.<br />
Kochi, J.K., Oxygen <strong>radical</strong>s, <strong>in</strong>: Kochi, J.K. (Ed.), Free Radicals, Vol. II, Wiley, New York<br />
(1973), Chapter 23, pp. 665-710 (a).<br />
Kochi, J.K, Oxidation-reduction reactions of free <strong>radical</strong>s and metal complexes, <strong>in</strong>: Kochi, J.K.<br />
(Ed.), Free Radicals, Vol. I, Wiley, NY (1973), Chapter 11, pp. 591-684 (b).<br />
Regitz, M. and Giese, B. (Eds.), C-Radikale Band E19a, Methoden der Organischen Chemie<br />
(Houben-Weyl), Thieme Verlag, Stuttgart (1989), pp. 547-548 (a).<br />
Regitz, M. and Giese, B. (Eds.), C-Radikale Band E19a, Methoden der Organischen Chemie<br />
(Houben-Weyl), Thieme Verlag, Stuttgart (1989), pp. 31-40 (b).<br />
Meiji Seka Kaisha, Ltd, European patent EP18415 (1982).<br />
Tosoh Corp., Japanese patent JP 11130708 (1999).<br />
Sumitomo Chemical Company, Ltd, European patent EP282221 (1992).<br />
Montaudon, E., Agorrody, M., Rakotomanana, F., Maillard, B., Intramolecular homolytic<br />
displacements. 15. Free-<strong>radical</strong> reactions to β-ethylenic <strong>peroxides</strong>, Bull. Soc. Chim. Belg. 96<br />
(10), 769-74 (1987).<br />
Maillard, B., Bourgeois, M.J., Montaudon, E., Lalande, R., French patent FR2628107 (1989).<br />
Mann<strong>in</strong>g, S.C. and Moore, R.B., Carboxylation of polypropylene by reactive extrusion with<br />
functionalized <strong>peroxides</strong> for use as a compatibilizer <strong>in</strong> polypropylene/polyamide-6,6 blends,<br />
Journal of V<strong>in</strong>yl & Additive Technology, 3 (2), 184-189 (1997).<br />
Akzo Nobel, patent WO 01/27078 (2001).<br />
9
VIII.<br />
Abbreviations<br />
Code Chemical name* CAS nr.<br />
BPIC Tert-butyl peroxy isopropylcarbonate (Trigonox BPIC) 2372-21-6<br />
BPO Dibenzoyl peroxide (Lucidol, Cadet) 94-36-0<br />
BTMHP Bis(3,5,5-trimethylhexanoyl) peroxide (Trigonox 36) 3851-87-4<br />
CPDC Dicetyl peroxydicarbonate (Perkadox 24) 26322-14-5<br />
DCP Dicumyl peroxide (Perkadox BC) 80-43-3<br />
DTAP Di-tert-amyl peroxide (Trigonox 201) 10508-09-5<br />
DTBP Di-tert-butyl peroxide (Trigonox B) 110-05-4<br />
EHP Bis(2-ethylhexyl) peroxydicarbonate (Trigonox EHP) 16111-62-9<br />
LPO Dilauroyl peroxide (Laurox) 105-74-8<br />
MPDC Dimyristyl peroxydicarbonate (Perkadox 26) 53220-22-7<br />
TBCPDC Bis(4-tert-butylcyclohexyl) peroxydicarbonate (Perkadox 16) 15520-11-3<br />
TBHP Tert-butyl hydroperoxide (Trigonox A) 75-91-2<br />
TBPB Tert-butyl peroxybenzoate (Trigonox C) 614-45-9<br />
TBPEH Tert-butyl peroxy-2-ethylhexanoate (Trigonox 21) 3006-82-4<br />
TBPIB Tert-butyl peroxyisobutanoate (Trigonox 41) 109-13-7<br />
TBPP Tert-butylperoxy pivalate (Trigonox 25) 927-07-1<br />
* Cadet, Laurox, Lucidol, Perkadox, Trigonox are tradenames of Akzo Nobel.<br />
10
IX.<br />
List<strong>in</strong>g of Organic <strong>peroxides</strong> from <strong>Acros</strong> <strong>Organics</strong><br />
<strong>Acros</strong> Cat no<br />
Chemical Name<br />
34988 Dicumyl peroxide, 99%<br />
10515 2,2'-Azobis(isobutyronitrile), 98%<br />
34993 Di-tert-butyl peroxide, 99%<br />
21178 Dibenzoyl peroxide, 75%<br />
34980 1,1-Di(tert-butylperoxy)cyclohexane, 50%<br />
34996 Cumyl hydroperoxide, 80%<br />
34974 Dilauroyl peroxide, 99%<br />
34994 3,6,9-Triethyl-3,6,9-trimethyl-1,4,7-triperoxonane, 41%<br />
34977 1,1--Di-(tert-Butylperoxy)-3,3,5-trimethylcyclohexane, 75%<br />
34983 2,2-Di(tert-butylperoxy)butane, 50<br />
34986 tert-Butyl peroxyacetate, 95%<br />
17014 tert-Butyl peroxybenzoate, 98%<br />
34985 tert-Butylperoxy 2-ethylhexyl carbonate, 95%<br />
34975 2,2'-Azobis(2-methylbutyronitrile), 98%<br />
34981 tert-Butyl peroxy-3,5,5-trimethylcyclohexane, 97%<br />
34984 tert-Butylperoxy isopropyl carbonate, 75%<br />
34989 di(tert-butylperoxyisopropyl)benzene, 96%<br />
34991 tert-Butyl cumyl peroxide, 95%<br />
34990 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane, 92%<br />
18034 tert-Butyl hydroperoxide, 80%<br />
34998 2,3-Dimethyl-2,3-diphenylbutane, 95%<br />
34997 3,4-Dimethyl-3,4-diphenylhexane, 98%<br />
Enter these product codes <strong>in</strong> the quick search box at www.acros.com to f<strong>in</strong>d out more about<br />
available packsizes.<br />
11
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NEW N o 48<br />
TBAF, Tetrabutyl Ammonium Fluoride, a mild fluor<strong>in</strong>ation reagent.<br />
Chemistry review pr<strong>in</strong>ts<br />
N o 1<br />
on Comb<strong>in</strong>atorial Chemistry :<br />
Solid Phase <strong>synthesis</strong> of compound libraries and their application <strong>in</strong> drug discovery by Mark<br />
A. Gallop, Affimax Research Institute,USA<br />
N o 2<br />
on Asymmetric Catalysis :<br />
From homogeneous to heterogeneous catalysis, recent advantages <strong>in</strong> asymmetric <strong>synthesis</strong><br />
with nitrogen conta<strong>in</strong><strong>in</strong>g ligands by F.Fache, P.Gamez, B.Dunjic and M. Lemaire, Institut de<br />
Recherches sur la Catalyse,UCBL-CPE,Villeurbanne, France.<br />
NEW N o 3<br />
on Carbocycles :<br />
1-Hydroxycyclopropanecarboxylic acid a ready available and efficient precursor.<br />
NEW N o 4<br />
Silylated N-Tert-Butyl Aldim<strong>in</strong>es : Versatile Organosilicon Reagents for Polyenals Synthesis.<br />
NEW N o 5<br />
A complete range (C2 to C20) of fully synthetical Sph<strong>in</strong>gos<strong>in</strong>es and Ceramides.<br />
NEW N o 6<br />
Organic Peroxides <strong>in</strong> Radical Synthesis Reactions<br />
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