Communication
exotherm onset temperature of 1048C. This finding was similar
to literature temperatures, although the Q in this study
testing was carried out in accordance with established proto-
[30]
cols, and three levels were tested: 0.045, 0.45, and 4.5 J.
DSC
À1
[27]
(
À553 calg ) was higher than reported. A TDSC and QDSC for
Briefly, a capacitor was charged to a defined potential (0.045,
0.45, or 4.5 J) and a pulse was applied to cause the potential
of the selected capacitor to form across the sample spark gap.
Typically values for the buildup of electrostatic energy on a
person are within the range of 0.005–0.08 J, which is enough
commercial 75% benzoyl peroxide has been reported, and the
energy released was low enough that, when stabilized with
2
5% water, this oxidant is predicted by Yoshida correlations to
[
28]
be impact sensitive, but not explosive. Commercial mCPBA
[21,31]
(
77%) was used herein, and provided an onset temperature of
to set off some primary explosives.
Phosphonium per-
À1
9
18C with a QDSC value of À527 calg . The T was in accord-
ruthenates ATP3 (7), MTP3 (8), and TP3 (9) all ignited at the
lowest setting, whereas TPAP (4) did not ignite even at the
highest setting of 4.5 J. Although the addition of stabilizing
agents appears to lower the impact and thermal sensitiveness
of IBX, both SIBX (5) and IBX (2) ignited at the second lowest
setting (0.45 J) along with benzoyl peroxide (10) and DDQ
DSC
ance with literature values, but the Q was again higher than
DSC
[
27,29]
that reported.
Unsurprisingly, both mCPBA and benzoyl
peroxide flagged as potentially impact sensitive and explosive.
Cerium ammonium nitrate (11), which reacted to the
hammer test with a change in color, had a high onset temper-
À1
ature of 2248C and a QDSC of À677 calg . Although, CAN had
(14). At the highest setting of 4.5 J, TEMPO (3), SO ·pyr (15),
3
the second highest TDSC of the oxidants tested, it also had the
third highest QDSC, behind IBX and PCC (16), and flagged as po-
tentially impact sensitive and explosive in Yoshida correlations.
Only four oxidants did not flag as potentially impact sensi-
tive and explosive: Oxone (12), MnO2 (13), DDQ (14), and
PCC (16), and DMP (1) ignited. Of these oxidants, only SO ·pyr
3
did not flag in the Yoshida correlations, suggesting a slightly
better safety profile than the others. Finally, with no ignitions
at 4.5 J were mCPBA (6), CAN (11), oxone (12), MnO (13), NBS
2
(17), and TPAP (4).
sulfur trioxide pyridine complex (SO ·pyr, 15). Of these, DDQ
and MnO2 did not show any exotherms below 3008C with
Combining the three sensitiveness test results clearly high-
lighted some oxidants as being more problematic than others.
IBX, benzoyl peroxide, and the phosphonium perruthenates
ATP3, MTP3, and TP3 are all sensitive to impact, as demonstrat-
ed by go events in the hammer test. All these oxidants dis-
played highly exothermic decomposition and ESD sensitive-
ness. In contrast, Oxone and manganese dioxide were benign
in every test, giving no-go events in hammer test, no ignition
at 4.5 J, and no (or small) exotherms in scDSC. These data ena-
bled classification of these two oxidants as having the best
safety profile of those tested.
3
DDQ melting and MnO not undergoing any thermal transi-
2
tions. The MnO sample appeared unchanged upon opening
2
the crucible. Oxone and SO ·pyr did display exotherms; howev-
3
er, their energy and onset temperatures were such that they
are below the Yoshida energy thresholds.
The remaining oxidants—TEMPO (3), PCC (16), and NBS
(
17)—are all flagged by Yoshida correlations with TDSC values of
1
82, 164, and 1318C, and Q
values of À464, À725, and
DSC
À1
À494 calg , respectively (Figure 3).
Electrostatic discharge (ESD) is the accidental stimulus that
is most likely to occur in a laboratory setting from human
static electricity (e.g., transferred through a metal spatula). ESD
To provide a ranked series (Table 1), the oxidants were
scored according to their sensitiveness testing results. For the
hammer test, a go event=1 and a no-go=0. For scDSC, being
flagged=1, whereas falling below the threshold is equivalent
to 0. For ESD testing, no ignition=0, ignition at 4.5 J=1, igni-
tion at 0.45 J=2, and ignition at 0.045 J=3. By using this
method, a higher final score indicates that the oxidant shows
increased sensitiveness and should be treated with more care.
However, the specific hazards should always be considered
before using any oxidant, for example mCPBA scores only 1,
but has an onset temperature below 1008C, so it should not
be used when elevated temperatures are required. Further-
more, in terms of handling some of the tested oxidants, one
must be mindful of potential sources of ignition that may be
presemt in the synthetic laboratory. For instance, the use of
earthed spatulas and conductive or antistatic containers may
be one way to mitigate the potential ESD risk when handling
oxidisers with low ESD sensitiveness; while the use of Teflon-
coated spatulas and avoiding ‘tapping’ spatulas may be one
way to mitigate risks when handling oxidants that exhibit
impact sensitiveness.
Figure 3. Yoshida plot of oxidants which exhibited exotherms under scDSC
analysis. All data was acquired with a heating rate of 58Cmin . Oxidants
In conclusion, the synthetic chemist relies heavily on a range
of oxidants to perform a vast array of synthetic transforma-
tions. The sensitiveness data provided herein contributes to
the understanding of the safety profile of some common oxi-
dants, and can thus be used when selecting appropriate re-
À1
above the blue line are considered potentially impact sensitive, with those
above the orange line potentially explosive. Thresholds used are 25% lower
than the original Yoshida thresholds to provide a more conservative predic-
[
19b]
tion as recommended by Sperry et al.
3
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