Korichnevvy Kahverengi: Faculty of Petrochemistry, Rasputin University, Nizhny Novgorod, Marroia de la Mierda: Pfister Ltd, Rostig von Braun and Günther Schlonk : School of Inorganometallics, University of West Failure
This manuscript is dedicated to the memory of Fuscus Browning
Abstract: One can’t judge a book by its cover, but one can judge a reaction by its colour.
Specific: Modern labs are replete with instruments and techniques for determining the complexity of crude reaction mixtures. TLC, NMR, IR, MS, the list goes on. These techniques all require a sample of material in question, and time to analyse it. Conspicuously absent from the illiterature is a rapid and non-destructive assay for the purity of a reaction mixture. Herein, we describe a technique for the instantaneous analysis of sample purity with visible light spectroscopy.
Today, green chemistry is all the rage. But before there was green chemistry, there was something murkier, more primal. Prior to the days of 0.001% catalyst loadings, flash column chromatography and click chemistry was a time of darkness. A time when Na metal reductions and fractional distillation were the norm. Today, we know this field as Brown Chemistry.1 Few remnants of this field persist in the modern chemical canon. After all, why would one conduct a Skraup synthesis of a quinoline when Smegma-Aldrich sells thousands of them?2 Despite the antiquated nature of this field, we believe there may yet be more to learn from it.
Many good things in this world are brown. Chocolate, coffee, good tilled earth.3 Alas, this is rarely true in the world of chemistry. Most compounds can undergo decomposition by forming larger, more conjugated molecules, with a greater capacity to absorb visible light than their parents. The endpoint in this chemical death spiral is brown sludge. Consider pyrrole (1), and its proclivity to commit chemical kamikaze (scheme 1).
A fresh bottle of pyrrole from Smegma Aldrich appears light yellow in colour. Upon exposure to most things, or even on exposure to nothing at all, pyrrole converts into a poorly defined, polymerised, oxidised sludge, which is roughly approximated as species 2. Figure 1 contains a second example of this trend. Each flask contains the crude product of an enamine reduction with scandalous sulphate (ScSO4).4 Which reaction do you think was more successful?
With pyrrole as an example, we propose the correlation between the “brownness” of a sample and its purity as the foundation of a new visible-light-based assay. This assay consists of a scale from one to ten, from “a whiter shade of pale” to “darkness my old friend” (figure 2). To honour the memory of our late colleague Fuscus Browning, we have dubbed this scale: The Browning Index.
The low end of the scale represents higher purity, such as that of commercially available fine chemicals. Conversely, a ten on the browning index suggests the purity of the sludge that accumulates at the bottom of a solvent waste bottle. Like most “rules” in chemistry, this index is a sweeping generalisation riddled with exceptions and inconsistencies. It is quite possible to obtain a compound that is both pure and brown, just as it is possible to have colourless impurities. However, it is more likely that a nine on the browning index is a shitshow at heart, as well as on the surface. Because each sample is shitter than the last, this index is technically a logarithmic scale.
To demonstrate the application of this index, we have compared three samples of the same molecule, with varied degrees of purity (Figure 3). Our molecule of choice was Klaxon-Smythe-Whine’s new antidepressant: Sulferalone®.5
Sample A rates at 3 on the Browning Index. Its spectrum indicates quite a high level of purity, with only a few contaminants poking their heads above the baseline. This is in stark contrast to sample B, which contains one major and several minor impurities. B comes in at a solid 6 on the index. Sample C, scores a 9, and its spectrum is best described as a kind of chemical skid-mark from 9–5 ppm. Spectroscopists know this as “the D. Parton effect”.6 C demonstrates a second characteristic of high-browning compounds: a viscosity like congealed despair. Samples A–C are in clear agreement with our proposed index: Browning Index and purity are inversely correlated. It should be noted, however, that we’ve obviously cherry-picked the data to support our claims.6.5
Continuing the theme of wholesale assumptions, we have compiled a table of suggested workup procedures commensurate with the Browning Index of a mixture (table 1).
Samples with Browning scores between 1 and 3 are typically good enough to use “without further purification,” provided one doesn’t look too closely. Beyond 3, some manner of purification is essential to prevent the impurities breeding. Mixtures below 5 are difficult to rectify without resorting to chromatography, with the number and length of columns increasing as one descends. An 8 lies on the borderline of recoverability. While it is sometimes possible to sift out a few mols of product from the slew of shyte, it is rarely worth the effort. A Browning Score of 9 usually means the starting material can only be reassembled by air crash investigators. Attempting to isolate something useful from such a train-wreck calls to mind those expressions about needles in haystacks and polishing turds. We advise that one call a priest to perform the last rites instead. A 10 on the Browning Index is reserved for those samples even a god couldn’t save. In such cases, the glassware is lost along with the starting material. To describe a 10 as “Passchendaele in a flask” would only be a mild exaggeration (as well as deeply insensitive). The only course of action is to incinerate the evidence, and carefully reconsider your life choices.
At this stage, some may wonder what The Browning Index has to offer over the many existing analytical methods. Clearly, reviewer 2 also held this opinion. While techniques like NMR and TLC can provide more detailed information about a mixture, they require two things that the Browning Index does not: a physical sample and time to analyse it. Preparing and running an NMR sample can take anything upwards of 15 minutes, and finding an appropriate TLC eluant is comparable. Analysis via the Browning Index is instantaneous: no sample preparation is required, nor any apparatus/instrumentation.
We should admit that we are not the first to have had this idea. Passing references are made to such a scale in Monty Python’s “The Life of Brown” and in Kermit the frog’s song “it’s not easy being beige”. In many related studies, renown Australian academic E. F. Tom has investigated the relationship between yellowness and purity, in relation to energetic materials.7a,b To the best of our knowledge, however, we are the first to categorise these trends into an easy-to use index. We feel able to make this claim because we haven’t bothered to check if anyone else has beaten us to it.
We have defined the Browning Index: the kind of ladder that the biblical Jacob could have used to climb out of a thunderbox. We hope this index will become a ubiquitous feature of chemistry labs worldwide. If disgusting brown sludge is a universal feature of chemistry (and it definitely is), then so too should be a way to describe it. In the immortal words of Mediocrates of Pfizantium: “everything turns brown in the end”.
Experimental data, spectra and reaction conditions are available from http://www.onlyfans.com/SchlonkItUp
K. K. used his experience in oil refining and coal tar extraction to define the 9 and 10 categories of the index. M. M. contributed fuck all. R. B. prepared the samples for figure 2, and used his training as a hostage negotiator to appease reviewer two. G. S. prepared the manuscript, and plenty of batches of brown goo.
Conflicts of Interest
Günther Schlonk is Imperial Editor in Perpetuity of The Journal of Immaterial Science. He reviewed this article while blind drunk, to avoid bias.
No graduate students were harmed in the preparation of this manuscript.‡
G. S. acknowledges the estate of aunty Gladys for funding this work, may she rest in peace.
Notes and references
1 S. Mawon, H. Kahawia, J. Brown Chem. 1927, 5, 30928375
2 Smegma Aldrich Spring Catalogue, 2021
3 S. Gamgee, B. Baggins, Middle J. Chem. T.A. 3018, 1, 13.
4 D. Blackburn, J. Immat. Sci. Mat. 2021, 1, 1.
5 The Smerck Index, 17, 3499 (Sulferalone)
6 D. Parton, J. Mus. Chem. 1980, 1, 1.
6.5 Just like everyone else.
7b https://www.reddit.com/r/ExplosionsAndFire/‡ Not remotely true
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