How are we doing boys n girls as the march towards Christmas draws ever closer. I spent this week buying Christmas presents and even picked myself up an early present. A chemistry book titled “The Periodic Table” by Primo Levi. The author is an Italian Jewish chemist and holocaust survivor. I haven’t finished this yet but the book is a collection of short stories based on the authors life and themed around a certain element. I will probably attempt a full review of this book once I’ve finished it but it certainly seems interesting for now.
I also picked up an old book as a Christmas present from the same shop and the books combined got me thinking about the smells of books, specifically the difference between old and new. And due to reasons I wrote about last week I’ve been away from my beloved fume hood much of this week so I thought I’d go over the various aromas from books. This is fitting as it also keeps in theme with last week’s blog on vanillin and the smell of Christmas. With that in mind let’s start with my new copy of The Periodic Table. This book , like all books new, (and old) will release many hundreds of volatile organic compounds (VOC’s). These originate from a variety of different factors, some directly and others indirectly through compound degradation. This may be from the specific type of paper that has been used and the type of paper making process. The binding and type of glue used, and the printing ink. A big topic right now is the use of Bisphenol A (BPA) in inks and its toxicity or lack thereof.
A molecule of BPA found in inks.
The VOC’s are what gives rise to the various smells of books. In newer books it’s probably safe to assume that the scents come exclusively from these primary sources and less from degradation.
In glues and adhesives, common VOC’s will arise from co-polymers. When a polymer is formed by a repeating chain of one molecule (or monomer) together it is termed a homopolymer. When two different types of monomers are joined in the same chain the resulting polymer is called a co-polymer. In hot melt adhesives the most common copolymer is Ethylene-vinyl acetate (EVA). This is the co-polymer of ethylene and vinyl acetate.
Vinyl acetate added to ethylene to give ethylene-vinyl acetate co-polymer.
During the paper making process, paper is treated with a number of different chemicals appropriately named… Paper chemicals. These modify the properties of paper to achieve desired qualities, such as colour, strength and water resistance.
Hypochlorite’s, chlorine and hydrogen peroxide are some chemicals used in bleaching paper, removing any lignin, itself a polymer from plant matter, that may remain.
Strengthening is achieved through numerous chemicals including urea formaldehyde, melamine and epichlorohydrin. All of which are particularly smelly!
From left to right: Urea formaldehyde, epichlorohydrin and melamine.
Alkyl ketene dimers are also employed to aid water resistance, and petrochemicals are also common as solvents for inks.
All of these are capable of releasing VOC’s and contribute to a books smell.
When we consider old books we must assume that these chemicals all breakdown over time to form different chemicals, releasing different VOC’s resulting in different odours. In old books there will also be new aromas resulting from the degradation of cellulose.
To sum up, the smell of books, old and new, is not from one overall molecule but a result of a cocktail of different compounds that arise from the manufacturing process and their degradation over time.
In response to the “you only chose German chemists” tweets, this week’s #ReactionRecap is the Bamford-Stevens reaction. Sometimes called Bamford-Stevens olefination, this is co-named from the British chemist William R Bamford and the Scottish chemist Thomas S Stevens. The reaction is utilized for the formation diazoalkanes and alkenes by the alkaline cleavage of tosylhydrazones in the presence of strong base. The mechanism of this goes through two different pathways dependent upon whether protic, or aprotic solvent is used. In protic solvent the reaction proceeds through the formation of a carbenium ion giving a mixture of E and Z isomers. In aprotic solvent the reaction proceeds through the formation of carbene and favours Z alkenes.
Barluenga developed the first example of employing these tosylhyrdrazones as nucleophilic partners in cross-coupling reactions. Typical nucleophilic reagents in cross-coupling reactions are organometallics such as organomagnesium, zinc, tin, silicon, and boron. Instead the tosylhydrazones, combined with (electrophilic) aryl halides, can be used to prepare poly-substituted olefins under Pd-catalysed conditions without the use of expensive organometallic reagents.
The scope of this coupling reaction is wide. Tosylhydrazones derived from aldehydes and ketones are well tolerated, giving rise to both di- and tri-substituted olefins. In addition, the variety of aryl halides are also well tolerated as coupling partners including those containing both electron-withdrawing and electron-donating groups, as well as π-rich and π-deficient aromatic heterocyclic compounds.
Hopefully next week I can talk about some chemistry I have done and not have to publish the beginings of a literature review of the chemistry of glue.
Well that’s your lot for today folks and hope you’ve taken away something useful going forward. Might actually get on and do some work with the rest of my day now…
Reach me @LewisMGooch