Reactions of Radioactive 18F with Alkenes, Alkynes, and Other

2 Reactions of Radioactive F w i t h Alkenes, Alkynes, and 18

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Other Substrates F. S. R O W L A N D ,

FLEET

RUST,

and J O A N P. F R A N K

Department of Chemistry, University of California, Irvine, C A 92717

18

Radioactive F atoms at tracer levels offer several special advantages, and some problems, in comparison with stable F atoms for the study of gaseous chemical reactions. Thermal fluorine atoms are exceedingly reactive with a wide variety of substrates (and surfaces), leading to a variety of experimental difficulties: (1-4) (a) the reactive, often corrosive, nature of many F atom sources; (b) the rapid abstraction of H from most hydrogenous substrates, with the formation of HF; (c) the exothermicity of many reactions, especially the formation of HF, with corollary problems of rapid, uncontrolled temperature rises; and (d) the high chemical reactivity of many product molecules, again including HF. The use of F atoms at tracer levels avoids several of these difficulties, permitting the systematic study of the reactions of atomic fluorine with many types of substrate molecules, e.g., alkenes and alkynes. 19

18

18

-1

Since F can be readily detected at mole fractions of 10 10 , many of the macroscopic problems of F chemistry simply do not occur. For example, glass containers never show visible etching; heat increases are always negligible; reactive products do not cause macroscopic corrosion, etc. At these -14

19

concentration levels certain corollary limitations are also o b served. Two F atoms do not react with one another, nor a r e two F atoms detectable in the same molecule. No macroscopic property of the molecule (e. g. infrared, NMR, etc.) can be used as an aid in identification of the qualitative or quantitative aspects of any of the products. The 110 minute half-life of F limits experiments to those that can be c a r r i e d to completion in a few hours. Further, the F atoms must be freshly produced for 18

18

18

18

©

0-8412-0399-7/78/47-066-026$10.00/0

Root; Fluorine-Containing Free Radicals ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2.

R O W L A N D

E T

Reactions of Radioactive

A L .

F

27

18

each experiment, and the F atoms emerging from nuclear reactions ordinarily have kinetic energies vastly in excess of thermal energies and this excess energy must be removed both to retain the atoms within the physical boundaries of the e x p e r i ment and to avoid confusion between thermal and hot atom r e a c tions in each particular system. O v e r a l l , then, the radioactive tracer F approach has a separate set of experimental advan tages and disadvantages, and studies with F can furnish i n f o r mation complementary to that obtained with stable F . In many instances, the F studies can readily furnish details not a c c e s sible to the macroscopic studies, and this review emphasizes some of the systems in which the F techniques have shown such utility. 1

8

1 8

1

8

1 9

1

8

1

8

Experimental Aspects of Radioactive

1 8

F Studies.

While several nuclear reactions are potentially available for the formation of F . most of the chemical studies described here have utilized F formed by the F ( n , 2 η ) F nuclear r e a c tion with fast neutrons, usually from a special fast neutron gen erator. Some studies have utilized t h e F ( ^ n ) F reaction, with results which are comparable to those from the (n, 2n) reaction, since the many inelastic collisions made p r i o r to reaching the chemical energv range completely erase the source and energy history of the F atoms at the time of chemical reaction. How ever, the accompanying radiation damage from the various nuclear methods for producing F is not necessarily c o m p a r able, and different distributions of F among various possible products can a r i s e from the presence of such radiation effects. 1 8

1

1 9

18

1 9

1 8

1 8

1 8

A discussion of the experimental aspects of F r e c o i l chemistry in the gas phase has been presented elsewhere («510),and only a brief summary follows. The F ( n , 2 η ) F r e a c tion is initiated by 14 M e V fast neutrons from a neutron gener ator (Kaman A 711). In the usual target arrangement an i r r a diation of twenty minutes forms approximately 1 m i c r o c u r i e of F from 0.3 grams of F source gas. The total absolute yield for F formation is routinely monitored through the measured F production in a standard (a sleeve of Teflon) surrounding the glass sample ampoule during irradiation. Comparison of absolute yields between duplicate samples shows that the r e p r o ducibility of irradiation is approximately 10%. The analysis of relative yields of products within a given sample can be c a r r i e d out much more accurately, with 1% reproducibility often 1

1 9

1 8

1

1

8

18

9

8

1 8


28

FLUORINE-CONTAINING

F R E E

RADICALS

attained. However, it is possible to detect compounds of which as few as 10 molecules have been made, and random statistical fluctuations become an important limitation in a manner not found with the 1 0 - 1 0 molecules formed i n typical m a c r o scopic experiments. 4

1 6

1 8

The F atoms formed in nuclear reactions can possess 10 electron volts of kinetic energy per atom (2 χ 10 k i l o c a l o r i e s / mole) and approximately 1-2 atmospheres of gas is necessary to remove this energy in a 1 cm path length. Consequently, either high pressures o r large containers are required, and the geom etry of the fast neutron source itself limits glass ampoules to about 2 cm diameter and 4 cm length for most of our e x p e r i ments. Loss of F from the gas phase by r e c o i l into the ampoule walls is unimportant (0.9 virtually a l l F reactions are attributable to thermal mechanisms with hot reactions sup pressed to about 1% or less (5-10). The thermalization of the F atoms can be accomplished in two ways: (a) through c o l l i sion with noble gases which are inert moderators (9,10);and (b) through collision with an excess of perfluorinated source gases which a r e inert toward reaction with thermal F atoms. The necessity for F as a target for the F ( n , 2 η ) F reaction requires that at least one major component of each system must be a fluorinated molecule, but some of these are chemically quite inert. T y p i c a l source gases which can also serve as moderators a r e N F , C F , S F and C F (12-15). 1

1

8

8

1

8

8

1

1

9

1 9

3

1 8

4

6

2

8

18

6

F Reactions with Alkene s and Alkynes.

The most widely studied F atom reaction system is that of F plus ethylene, which was initially studied for the purpose of using ethylene as a scavenger in C F systems, and more recently with interest in the excited fluoroethyl radical i n t e r mediate. Studies using widely different sample preparation procedures and irradiation conditions are mutually consistent, ( 9 , 1 0 , J13) and have demonstrated that the kinetics of the F atom reactions under study are independent of their irradiation history. 1

1

8

8

4

1

8

In the f i r s t study, valuable information concerning the e l e mentary processes involved in the reactions of atomic fluorine with ethylene was obtained from C F - C H mixtures with F atoms formed by the F ( y , n ) F reaction in C F (9, 10). The F atoms which failed to react with C F were effectively removed by addition to ethylene, as i n Equation 1. The 4

1 9

1 8

2

1

4

1 8

4

4


8

30

FLUORINE-CONTAINING

1 8

F

+ CH =CH 2

>€H

2

2

1 8

F R E E

FCH *

RADICALS

(1)

2

subsequent fate of these C H F C H radicals was then determined by a pressure-dependent competition between stabilization, (equation 2) and decomposition, (equation 3). The stabilized 2

CH

2

FCH*

1 8

1 8

2

+ M

•CH

CHg FCH*

2

1 8

FCH

+ M

2

(2)

•CH F=CH + H

1 8

1 8

(3)

2

C H F C H radical was then detected after reaction with scavenger molecular I as C H g F C H I (equation 4). 2

A

8

2

1 8

2

CH

2

1 8

FCH

2

+ I

2

•CH

2

2

1 8

FCH I 2

+ I

(4)

The linear pressure dependence of the C H F C H to C H g F C H I ratio in excess C F further showed that the C H g F C H * radicals were almost uniformly monoenergetic indicating that the radicals received negligible additional excitation from extra translational energy of the F atom (see below). A s i m i l a r F atom addition-plus-decomposition mechanism has been invoked to explain the presence of C H F as a product from the photolysis of O N F in the presence of C H (16). 1 8

1 8

2

2

1 8

4

2

1

8

2

3

2

4

M o r e recently, Rowland and coworkers reported the results of some experiments on fluorine atom additions to olefins and acetylene using t r a c e r levels of F generated by the F ( n , 2n)F reaction (5-8,12-15). These experiments were c a r r i e d out under more nearly ideal conditions: (a) the ampoule contents suffered negligible radiation damage because of the low level of radioactivity p e r sample; (b) hot reactions of F were reduced to 1, the o b s e r v a tion of concave curvature upward instead of the straight lines of Figure 2 serves as a diagnostic test for "weak" collisions. 4

2

4

3

2

9

4

4

2

4

2

4

4

2

4

The reactions of t h e r m a l F atoms with alky ne s are analo gous to the alkene reactions just described. The F atoms add rapidly (17) to acetylenic bonds, as illustrated in (8) and (9) (7). 1 8

1

8


FLUORINE-CONTAINING

F R E E

ro p 5

5

t

SF % 5

ΑI

18 CH 'CH F

*

CHïC F l8

2

I

8

10'

£ ζ Ο

2

υ

3 10

Figure 1. Radio gas chromatographic separation of CH — CH F from F(n, 2n) F reaction in gaseous SF -C H -HI mixtures (27) 2

18

19

18

6

2

2

• CF + C H +HI 4

2

4

(lOVPRESSURE) torr"

1

Figure 2. Ratio of decomposition stabilization vs. pressure" for Flabeled products from F reactions with C H, in excess CF (all samples contained CF :C H in the approximate ratio 18/1). Ο = C H F/CII ICH F with I as scavenger at 25°C (10). 1

18

k

2

18

3

2

18

2

2

2

t

18

h

h

2


RADICALS

2.

R O W L A N D

Reactions of Radioactive F

E TA L .

1 8

F

33

18

+ HC=CH —

CH=CH F 1 8

*HC

+ HI

1 8

F=CH

•*CH =CH F 18

2

(8) + I

(9)

Addition to ethylene is 0. 8 3 ± 0 . 0 2 as fast as addition to acetylene, as determined by experiments in which both ethylene and acetylene are simultaneously present and directly competing with one another (18). Product Analyses and Identification of Reaction Channels. A l l of the interpretations which follow are based on the assumption that the reacting F species is in the neutral, ground electronic state, designated as hot if it possesses excess kinetic energy and thermal if it does not. The possibility that the resulting species i s occasionally either charged or electronically excited cannot be rigorously excluded. However, the general reaction pattern of F from nuclear r e c o i l , especially the yield behavior i n the presence of inert moderators of varying ionization potential, has not yet furnished any evidence inconsistent with the hypothesis of the neutral, ground state as the reacting entity (9,10, 19-23). The very high energies for the f i r s t excited electronic state (12. 7 e V above the ground state) and the ionization l i m i t (17.4 eV) make appreciable fractions of these species very unlikely at energies comparable to chemical bond energies, while the hot reactions of F are almost entirely suppressed by the use of moderators. The observation of normal D / S behavior (equation 7) f o r radicals such as C H FC H * is good evidence for the absence of severe complications from the reacting species (13). 1

1

8

8

1

8

2

1 8

2

Typical data for the systems, C H / C F / H I and C H / S F / H I are contained in Table I (13). Additional data for the S F / C H (18:1)system are included in the D / S vs ( P ) " plot of Figure 3 (24). The extrapolated pressure for half-stabilization obtained from Figure 3 is 80 T o r r . F l o r e s and Darwent (16) also measured the stabilization of C H F C H * and found that pressures of about 100 T o r r were required. In their photolysis system, however, product analyses were difficult and accurate pressures for half - stabilization were not obtained. 2

4

4

2

4

6

6

2

4

1

2

A s seen from Table I, yields of about 60% are found f o r the addition of thermal F to C H at high p r e s s u r e s . The e x p e r i ments at pressures less than 1000 T o r r clearly show the loss of 1

8

2

4


FLUORINE-CONTAINING

F R E E

RADICALS

0.30Γ

!0 /P (TORR) 3

Figure 3. Ratio of decomposition/stabilization (D/S) vs. pressure" for F-labeled products from F reactions with C H, and C D, in excess SF . All samples contained SF /C H, or C D /HI in the approximate ratios 18/1/0.2. With the exception of two points at W/F (torr) = 1.00, the C H^ data are taken from Ref. 7. 1

18

18

6

2

6

2

(

2

t

2

t

k

2


2.

ROWLAND

E T


AL.

F

35

1S

energetic F into the ampoule walls because of insufficient available path length for removing the 10 eV of initial kinetic energy from the (n, 2n) reaction. The minor yield of CH3 1 8 F is caused by the direct hot substitution reaction (6). Most of the "missing" F in the high pressure samples has formed H F by abstraction of H from C H (equation 10). The H F so formed reacts on the ampoule wall and is not detected by normal radio gas chromatographic techniques. 1

8

e

1 8

1 8

2

1 8

F

1 8

4

+ CH;rCH

•H

2

1 8

F

+ CHjrCH

(10)

In general, at least half of the thermal F atoms can be expected to add to olefinic or acetylenic substrates with the formation of the corresponding radicals. Stabilization of these excited radicals is favored by high pressures (or by condensed phase experiments) although some radicals undergo even more decomposition at low pressures than observed with C H F C H (17). In most systems the radicals stabilized by collision with S F can usually be converted to the corresponding hydrocarbon by reactions with scavengers in analogy with equation (5). 1

8

1 8

2

2

6

Table I. Volatile Radioactive Products from F Atom Reactions in T y p i c a l Mixtures of C H with C F o r S F 1

2

4

8

4

6

(13).

Pressure, T o r r CF SF

1480

4

570

232 3840

6

C H 2

4

HI

1570

287

94 5

83

31

13

209

87

16

17

6

2

42

17

3

Product Yields, % Absolute CF

3

F

1 8

CHF

1 8

2

2.24 F

0. 58

CH3 F 18

CH F=CH 1 8

CH CH 3

SF

5

1 8

F

2

1 8

F

2

5.61 58.7

1.90

1 8

F

2.33

0.21

0.22

0.32

0.52

10.6

17.9

47.9

32.9

0.21

0.20

1.67

3.0

11.2

16.9

59.0

45.2

23.0

53.2 1.29

1.06

0.35

1.09


0.3

36

FLUORINE-CONTAINING

F R E E

RADICALS

Absolute Rate and C r o s s Section Measurements. A . Absolute Rate Measurements: The direct abstraction of H atoms from saturated hydrocarbons by fluorine atoms occurs very rapidly, with the formation of H F . The reaction of F with C H by Equation 11 leads to a product ( H F ) which is 1 8

1 8

4

1 8

F + CH —•H^F + CH 4

(11)

3

not readily analyzed by gas chromatography because of its high chemical reactivity. Direct chemical detection of such H F has been c a r r i e d out by Root e t . a l . ( 25 ). In our own experiments, the rate of reactions such as Equation 11 has been estimated by its competitive diminution of the yields of reactions with ethy lene o r acetylene (26, 27). The absolute rate constant of the corresponding F reaction with C H was determined indepen dently in a flow system using mass spectrometric detection and accurately measured flows of very s m a l l amounts of the r e a c tant gases (28). Fluorine atoms, free of F , were generated by the reaction of Ν atoms with N F (29). The rate constant with F was determined to be 7.1 χ 1 0 ^ * cm M o l e c u l e * " s e c " at 283°K, or reaction in about 1 of every 5 collisions with C H . Since the ratio of Η atom abstraction from C H versus addition to H C E C H was measured to be 0.41, (26,27) the absolute value for the rate of thermal F atom addition to H C E C H is about 1.7 χ 1 0 ' ° c m M o l e c u l e " s e c " . Similarly, the absolute rate constant for thermal F atom addition to ethylene can be estimated from the relative rates of addition to H C E C H versus C H = C H to be 1.4 χ l O ' ^ c n ^ m o l e c u l e ^ s e c " . Addition to both C H and C H thus requires three collisions or less on the average. 1 8

1 9

4

2

2

1 9

1

1

4

4

1

1

1

2

1

2

2

2

2

4

The relative rate constant ratio for addition of thermal F to ρ erf luo rop ropy lene to abstraction by thermal F of Η from H , has been measured by Grant (25) to be k c F / H °· 0.002 exp(1502 ± 1 7 c a l / m o l ) / R T . Rowland and Williams (27) have measured the rate constants of thermal F atom a b s t r a c tion of Η from H and C H relative to addition of F to H C = C H . T h i s ratio, measured to be 0.14: 0.41:1.0, may be combined with the results of Wagner et. a l . (28) to yield an absolute value of 2.0 χ 1 0 " * c m m o l e c u l e " s e c for k^ p . Rowland and Milstein (30) found that the initial F adcfition step is approxi mately equal in rate for C H and CHC1=CHC1 and about six times slower for CFC1=CFC1. With both C F C F = C F and CFC1=CFC1 addition is considerably slower than with olefins containing 1 8

1 8

2

3

6

k

2

=

1 8

2

11

3

1 8

4

1

1

3

1

2

8

2

3

2


0

5

6

±

2.

R O W L A N D

E T


A L .

F

37

18

fewer F and more H atoms. While such reactions are a l l veryrapid, and are reasonably consistent with one another, Grant and Root (31) have pointed out that certain inconsistencies do exist in the calculation of A r r h e n i u s parameters for the reactions of F with C F H , C H , H and C F , based on the measurements of Wagner et.al.(28). Nevertheless, Foon and Kaufman (32 ) believe that Wagner s result is the preferable one at this time. Work in the area of absolute rate constant determinations f o r fluorine atoms is still generally in the preliminary stage. The nature of tracer F experiments makes direct absolute rate determinations very difficult, while facilitating relative rate measurement. Measurements with F at various temperatures will eventually be important, and Root et a l . have already c o n structed a target that can be used with cyclotron-produced fast neutrons at temperatures as high as 475 Κ (33). 3

4

2

3

6

1

1

8

1

8

Β. C r o s s Section Measurements: In recent years crossed molecular beam techniques have been employed by Lee and c o workers (34) to study extensively the reactions of fluorine atoms with several different olefins. Very high cross-sections were observed, consistent with the rapid thermal rate constants measured above. In these experiments, multichannel decompo sition is observed (i. e., loss of Η o r C H after F addition to the ff-bond). Since the C - F bond is stronger than any other single bond with a carbon atom, C - F bond scission back to the original reactants does not compete with the exothermic p r o c e s ses involving breakage of C - C and C - H bonds. A tabulation of ΔΗ values for addition reactions of thermal F to various o l e fins is included (Table II) (6) Some highly endothermic path ways are listed for the purposes of comparison. The e x p e r i mental measurements of D / S in this table confirm that the only radicals undergoing appreciable C - C bond rupture with carbene formation after thermal F addition are those that form C F . The extraordinary stability of the C F radical makes C - C bond rupture exothermic for these radicals. 1 9

3

1

8

#

1 8

2

2

A summary of some average product translational energies and reactive cross sections is presented in Table HI (34, 35). According to L e e and coworkers, the higher average t r a n s l a tional energies typical of C H release reactions can be attributed to a higher potential energy b a r r i e r in the exit channel, under the assumption that some of the excess potential energy over that necessary for dissociation is converted into product t r a n s lational energy. In a l l of the cases listed in Table LÏÏ the c r o s s 3



2

2

2

2

CH =CH

2

2

CH =CHF

CHF=CHF (trans)

2

CH =CF

CHF=CF

2

Olefin CF =CF

2

1 8

2

2

2

2

1 8

FCH

1 8

2

2

2

1 8

1 8

2

2

2

2

2

2

2

2

2

1 8

1 8

18

2

1 8

18

1 8

2

1 8

1 8

1 8

2

2

2

2

2

CH F=CHF+ F CF F=CHF + H C H F +' C H F CH F=CHF+ H CHF F+ CH CH F=CH + F CF F=CH + H CH F + CH CH F=CH + H

1 8

2

1 8

1 8

1 8

1 8

2

1 8

1 8

1 8

f 8

1 8

2

(a) Reactions of hot and thermal

CH

2

FCHF

1 8

1 8

1 8

1 8

1 8

l B

CHF FCH

CH

2

2

2

2

Radical CF FCF

Decomposition products CF F+ CF CF F=CF + F CHF FCF CHF F+ CF CH F=CF + F CF F=CF +H CF FCHF CF F+ CHF CF F=CHF + F CH FCF CH F+ CF CH F=CF + H CF FCH C F F + CH CF F=CH + F CHF FCHF CHF F+ CHF

18

,

1 8

1 0 " s e c , long enough for several rotational periods. Even when the initial F atom has kinetic energy of 15 k c a l / m o l e , the forward-backward symmetry is maintained (56). 2

2

4

3

2

3

2

3

2

2

4

11

The infrared chemilumineseence experiments of McDonald et a l . demonstrate that the infrared quanta emitted (time scale ~ 1 0 " s e c . ) by the vibrationally-excited C H F or C D F products from F + ethylene are not characteristic of molecules with energy fully equilibrated in all degrees of freedom. T h i s lack of energy equilibration within the molecule, however, applies to C H F species vibra tionally-excited with about 10 k c a l / m o l e of excitation energy, and not to the C H F ^ species with about 50 k c a l / m o l e excitation energy p r i o r to H atom loss. Experiments with more highly vibrationally excited C H F m o l e cules (e. g. from F + C H B r ) do indicate equilibration of energy p r i o r to infrared emission (57). 3

2

2

3

2

3

3

2

4

2

2

3

3

Summary and Comments . The technique of using thermalized F atoms for the study of fluorine atom reactions has proven very useful with unsaturated hydrocarbons and halocarbons, providing data on mechanisms, relative rate constants and factors controlling such reactions. The characteristic difficulties cf macroscopic fluorine chemistry are often avoided at tracer levels, and analysis by radio gas chromatography can be quite straightforward. However, experiments at pressures below 0.1 atmosphere are relatively difficult, and most of the usual analytical methods are inapplicable at product mole fractions < 1 0 " . 1

8

1 0

Finally, many other classes of compounds can be readily substituted for alkenes and alkynes with little variation in equipment and technique. The extension to study of F atom 1 8


56

FLUORINE-CONTAINING

F R E E

RADICALS

reactions with organometallic compounds i s only one example of the broad applicability of t r a c e r F studies. A s interest i n the reactions of atomic fluorine continues to intensify, the r a d i o active F technique promises to be one of the important comple mentary approaches through which progress will continue. 1

8

1 8

Acknowledgment. This work has been supported by U . S . E . R . D . A . Contract No. AT(04-3)-34, Project Agreement No. 126. Literature Cited

1. Fettis,J.C.,Knox, J.H., Progr.React.Kinet. (1960), 2, 1. 2. Foon, R., Reid,G.P.,Trans.Faraday Soc. (1971), 67, 3513. 3. Homann, Κ.Η., Solomon, W.C., Warnatz, J., Wagner, H. G. Zetzsch, C., Ber.Bunsenges.Phys.Chem. (1970), 74, 585. 4. Kapralova, G.A., Margolin, A.L., Chaikin, H.M. Kinet. Catal. (1970),11,669. 5. Smail, T., Miller, G., Rowland, F.S., J.Phys.Chem. (1970), 74, 3464. 6. Smail, T., Iyer, R.S., Rowland, F.S., J.Amer.Chem.Soc. (1972), 94, 1041. 7. Williams, R.L., Rowland, F.S., ibid. (1972), 94, 1047. 8. Iyer, R.S., Ph.D. Thesis, University of California, Irvine, 1974. This thesis, entitled "Hot and Thermal Reactions of Atomic F in the Gas Phase", contains the most complete description of F recoil chemistry as practiced by Rowland and coworkers. 9. Colebourne, N., Todd, J.F.J., Wolfgang, R., Chemical Effects of Nuclear Transformations, Vol.1, International Atomic Energy Agency, Vienna, 1965,p149. 10. Todd, J.F.J., Colebourne, Ν., Wolfgang, R., J.Phys. Chem. (1967), 71, 2875. 11. Lee, J.Κ., Lee, E.K.C., Musgrave, B., Tang , Y.-Ν., Root, J.W., Rowland, F.S., Anal.Chem. (1962), 34, 741. 12. Williams, R.L., Iyer, R.S., Rowland, F.S., J.Amer. Chem.Soc., (1972), 94, 7192. 13. Williams, R.L., Rowland, F.S., J.Phys.Chem. (1972), 76, 3509. 14. Frank, J.P., Rowland, F.S., J.Phys.Chem. (1974), 78, 850. 15. Frank, J.P., Rust, F., Rowland, F.S., Physical Chemistry Paper 87, 170th Meeting of the American Chemical Society, Chicago, August 1975. 18

18


2.

ROWLAND

ET

AL.

Reactions

of

Radioactive

57

F

18

16. Flores, A.L., Darwent, Deb.B., J.Phys.Chem. (1969), 73, 2203. 17. Rowland, F.S., Cramer, J.Α., Iyer, R.S., Milstein, R., Williams, R.L., "Synthesis of F-Labelled Compounds by Direct Reactions of Atomic F in Radiopharmaceuticals and Labelled Compounds", Vol. 1, International Atomic Energy Agency, Vienna, 1973. 18. Milstein, R., Williams, R.L., Rowland, F.S., J.Phys. Chem. (1974), 78, 857. 19. Flores, A.L., Darwent, D. deB., J.Phys.Chem. (1968), 72, 3407. 20. Anbar, M., Neta, M., J.Chem.Phys. (1962), 37, 2757. 21. Spicer, L., Todd, J.F.J., Wolfgang, R., J.Amer.Chem. Soc. (1968), 90, 2425. 22. Tang, Y.-N., Rowland, F.S., J.Phys.Chem. (1967), 71, 4576. 23. Tang, Y.-N., Smail, T., Rowland, F.S., J.Amer.Chem. Soc. (1969), 91, 2130. 24. Frank, J.P., Rust, F., Rowland, F.S., unpublished experiments. 25. Grant, E.R., Ph.D. Thesis, University of California, Davis, 1975, Grant, E.R., Root, J.W., Chem. Phys. Lett. (1974), 27, 484; Manning, R.G., Grant, E.R., Merrill, J.C., Parks, N.J., Root, J.W., J.Chem. Kinetics (1975), 8, 39. 26. Williams, R.L., Rowland, F.S., J.Phys.Chem. (1971), 75, 2709. 27. Williams, R.L., Rowland, F.S., J.Phys.Chem. (1973), 77, 301. 28. Wagner, H.Gg., Warnatz, J., Zetzsch, C., An.Asoc. Quim.Argent., (1971), 59, 169. 29. The chemistry of F is similar to that of F. 30. Milstein, R., Rowland, F.S., Physical Chemistry Paper 134, 167th Meeting of the American Chemical Society, Los Angeles, April 1974. 31. Grant, E.R., Root, J.W., J.Chem.Phys. (1975), 63, 2970. 32. Foon, R., Kaufman, M., Progr.React.Kinet. (1975), 8, 81. 33. Parks, N.J., Krohn, K.J., Root, J.W., J.Chem.Phys. (1971), 55, 2690. 34. Parson, J.M., Shobatake, K., Lee, Y.Τ., Rice, S.A., Disc. Faraday Soc.(1973), 55, 344. 18

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35. Parson, J.M., Lee, Y.T., J.Chem.Phys. (1972), 56, 4658. 36. Bumgardner, C.L., Lawton, E.L., McDaniel, K.G., Carmichael, H., J.Amer.Chem.Soc. (1970), 92, 1311. 37. Frank, J.P., later improved unpublished results; see references cited in (12). 38. Cvetanovic, R.J., Advan. Photochem. (1963), 1, 157. 39. Tyler, S., Frank, J.P., Rowland, F.S., unpublished results. 40. Harrington, R.E., Rabinovitch, B.S., Frey, H.M., J. Chem.Phys. (1960), 33, 1271. 41. Kerr, J.A., Parsonage, M.J., "Evaluated Kinetic Data on Gas Phase Addition Reactions", Butterworths, London, 1972,p12. 42. Haszeldine, N., Steele, B.R., J.Chem.Soc., (1957),2800. 43. Libit, L., Hoffmann, R., J.Amer.Chem.Soc. (1974), 96, 1370. 44. Lee, F.S.C., University of California, Irvine, private communication. 45. Bumgardner, C.L., McDaniel, K.C., J.Amer.Chem.Soc. (1969), 91, 1032. 46. Bumgardner, C.L., Lawton, E.L., Acc. Chem.Res. (1974), 7, 14. 47. Williams, R.L., Rowland, F.S., unpublished results. 48. Lee, F.S.C., Rowland, F.S., unpublished results. 49. Frank, J.P., Rowland, F.S., J.Phys.Chem. (1974), 78, 850. 50. Setser, D.W. in "MTP International Review of Science, Physical Chemistry", Vol. 9, Butterworths, London, 1972, p 1. 51. Rabinovitch, B.S., Thrush, B.A., J.Phys.Chem. (1971), 75, 3376. 52. See, for example, Georgakakos, J.Η., Rabinovitch, B.S., McAlduff, E.J., J.Chem.Phys. (1970), 52, 2143. 53. Atkinson, R., Thrush, Β.A., Proc.Roy.Soc. A 316, (1970), 123, 131, 143. 54. Topor, M.G., Carr, Jr., R.W., J.Chem.Phys. (1973), 58, 757. 55. Mutch, W., Root, J.W., private communication; Mutch, W., Ph.D. Thesis, University of California, Davis, 1973. 56. Farrar, J.M., Lee, Y.T., J.Chem.Phys. (1976), 65, 1414. 57. Moehlman, J.G., Gleaves, J.T., Hudgens, J.W., McDonald, J.D., J.Chem.Phys. (1974), 60, 4790. Root; Fluorine-Containing Free Radicals ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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