Maybe NFS doesn't work well? Bear in mind that bonds from a second-period element to fluorine are generally stronger and less labile than the corresponding bonds to heavier halogens. If that's true, getting fluorine off a nitrogen-fluorine bond requires more work than, say, getting bromine off a nitrogen-bromine bond.
In https://en.m.wikipedia.org/wiki/Electrophilic_fluorination#Mechanism_and_stereochemistry several common fluorinating reagents are given, these being the compounds mentioned by the OP. The listed compounds all withdraw electrons from the nitrogen-fluorine bond more strongly than the carbonyl groups would in NFS (they use sulfonyl groups or a cationic function), so it seems this attribute is necessary to get the fluorination to go.
Maybe NFS doesn't work well? Bear in mind that bonds from a second-period element to fluorine are generally stronger and less labile than the corresponding bonds to heavier halogens. If that's true, getting fluorine off a nitrogen-fluorine bond requires more work than, say, getting bromine off a nitrogen-bromine bond.
In https://en.m.wikipedia.org/wiki/Electrophilic_fluorination#Mechanism_and_stereochemistry several common fluorinating reagents are given, these being the compounds mentioned by the OP. The listed compounds all withdraw electrons from the nitrogen-fluorine bond more strongly than the carbonyl groups would in NFS (they use sulfonyl groups or a cationic function), so it seems this attribute is necessary to get the fluorination to go.
Nice. Also, Id posit that since fluorine is the most electronegative halide, getting a compound $\ce{X-F}$ to act as a source of $\ce{F+}$ is harder than getting a compound $\ce{X-I}$ to act as a source of $\ce{I+}$. Hence, again, a more electron-withdrawing $\ce{X}$ moiety is needed.More
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The synthesis of NBS and NIS involve adding succinimide, the relevant halogen and NaOH (and AgNO3 in the case of NIS) in water. Fluorine reacts very violently with both oxygen and water forming HOF and FOOF, both highly toxic and explosive compounds. Water is thus an incompatible solvent for running fluorinations, you need a polar aprotic solvent such as MeCN. Secondly, in the presence of base, fluorine could undergo alpha-fluorinations to the carbonyl depending on the pKa of the C-3 and C-4 hydrogens.
The synthesis of NBS and NIS involve adding succinimide, the relevant halogen and NaOH (and AgNO3 in the case of NIS) in water. Fluorine reacts very violently with both oxygen and water forming HOF and FOOF, both highly toxic and explosive compounds. Water is thus an incompatible solvent for running fluorinations, you need a polar aprotic solvent such as MeCN. Secondly, in the presence of base, fluorine could undergo alpha-fluorinations to the carbonyl depending on the pKa of the C-3 and C-4 hydrogens.
NFS has a very similar N-F bond strength in MeCN to N-fluoroquinuclidinium (also a pain), so might work. But I think its just much more difficult to make then NFOBS/ NFSI which do just as good a job.More
You can get NFS from a heavier halogen counterpart plus silver fluoride. But that does not actually mean it will work as a fluorinating agent, which I suspect is the real problem.More
Maybe NFS doesn't work well? Bear in mind that bonds from a second-period element to fluorine are generally stronger and less labile than the corresponding bonds to heavier halogens. If that's true, getting fluorine off a nitrogen-fluorine bond requires more work than, say, getting bromine off a nitrogen-bromine bond.
In https://en.m.wikipedia.org/wiki/Electrophilic_fluorination#Mechanism_and_stereochemistry several common fluorinating reagents are given, these being the compounds mentioned by the OP. The listed compounds all withdraw electrons from the nitrogen-fluorine bond more strongly than the carbonyl groups would in NFS (they use sulfonyl groups or a cationic function), so it seems this attribute is necessary to get the fluorination to go.
Maybe NFS doesn't work well? Bear in mind that bonds from a second-period element to fluorine are generally stronger and less labile than the corresponding bonds to heavier halogens. If that's true, getting fluorine off a nitrogen-fluorine bond requires more work than, say, getting bromine off a nitrogen-bromine bond.
In https://en.m.wikipedia.org/wiki/Electrophilic_fluorination#Mechanism_and_stereochemistry several common fluorinating reagents are given, these being the compounds mentioned by the OP. The listed compounds all withdraw electrons from the nitrogen-fluorine bond more strongly than the carbonyl groups would in NFS (they use sulfonyl groups or a cationic function), so it seems this attribute is necessary to get the fluorination to go.
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The synthesis of NBS and NIS involve adding succinimide, the relevant halogen and NaOH (and AgNO3 in the case of NIS) in water. Fluorine reacts very violently with both oxygen and water forming HOF and FOOF, both highly toxic and explosive compounds. Water is thus an incompatible solvent for running fluorinations, you need a polar aprotic solvent such as MeCN. Secondly, in the presence of base, fluorine could undergo alpha-fluorinations to the carbonyl depending on the pKa of the C-3 and C-4 hydrogens.
The synthesis of NBS and NIS involve adding succinimide, the relevant halogen and NaOH (and AgNO3 in the case of NIS) in water. Fluorine reacts very violently with both oxygen and water forming HOF and FOOF, both highly toxic and explosive compounds. Water is thus an incompatible solvent for running fluorinations, you need a polar aprotic solvent such as MeCN. Secondly, in the presence of base, fluorine could undergo alpha-fluorinations to the carbonyl depending on the pKa of the C-3 and C-4 hydrogens.
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