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elementcollector1
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[*] posted on 13-8-2013 at 19:05


Does Schweizer's Reagent react with red phosphorus? (I know, cook question, but I can't exactly find a reference...)



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sonogashira
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[*] posted on 14-8-2013 at 13:50


How small can the incident area of a laser beam be made, in theory and in practice?
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elementcollector1
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[*] posted on 14-8-2013 at 14:20


Quote: Originally posted by sonogashira  
How small can the incident area of a laser beam be made, in theory and in practice?

If I had to guess...
In theory: 1 photon wide
In practice: Microscopic (search 'optical tweezers')




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[*] posted on 15-8-2013 at 07:22


Im thinking of getting a hotplate stirrer for distillations/refluxes as its hard to get good control of temperature with an open flame...
would a maximum temperature of 350'C work for most common laboratory procedures?
is 350'C sufficent to concentrate sulfuric acid past 95% concentration?
and is there a significant diffrence between aluminium and ceramic top plates?
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[*] posted on 15-8-2013 at 09:30


sonogashira:

See the link regarding AIRY disk.

http://en.wikipedia.org/wiki/Airy_disk

In essence, the shorter the wavelength, the smaller the spot (which is why Blu-Ray holds much more data than the DVD which is written (or meant to be read) by a red laser beam.

No matter the wavelength, a single photon sized spot is absolutely out of the question.

This has applications in the real world as well, note how even cellphone cameras are reaching very high mega-pixel counts? At some point the sensors cannot be made any smaller because the airy disk will cover adjacent cells, rendering further increases in sensor pixel density useless.

Ergo, the sensors have a finite minimum size, after which the senor size must increase to utilize the comparatively "large" dot the airy disk represents for small image features you wish to preserve.

DAS

[Edited on 15-8-2013 by Varmint]
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watson.fawkes
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[*] posted on 15-8-2013 at 10:13


Quote: Originally posted by Varmint  
At some point the sensors cannot be made any smaller because the airy disk will cover adjacent cells, rendering further increases in sensor pixel density useless.
This is true about geometrical optics, the model in which the Airy disc sits. It's not quite the same with diffractive optics, or other optical models.

But if you're using an ordinary lens with its de facto aperture, I have nothing to disagree with invoking the Airy disk.
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UnintentionalChaos
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[*] posted on 15-8-2013 at 11:23


Nobody seems to find my questions in these threads, but I am looking to t-Butylate a primary amine (specifically GABA). Can anyone suggest reaction conditions?



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sonogashira
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[*] posted on 15-8-2013 at 12:38


Thank you Varmint.


"t-Butylate a primary amine (specifically GABA)."
You may make it via THF to Cl(CH2)4OH [with HCl] to Cl(CH2)3COOH to your amine, alternatively. Or GBL to the chloride directly.



[Edited on 15-8-2013 by sonogashira]
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UnintentionalChaos
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[*] posted on 15-8-2013 at 18:28


Quote: Originally posted by sonogashira  


"t-Butylate a primary amine (specifically GABA)."
You may make it via THF to Cl(CH2)4OH [with HCl] to Cl(CH2)3COOH to your amine, alternatively. Or GBL to the chloride directly.


Disregard the post that used to be here. Found http://www.sciencemadness.org/talk/viewthread.php?tid=8477

Get the distinct impression that it's not happening and I need an alternate route.

[Edited on 8-16-13 by UnintentionalChaos]




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[*] posted on 16-8-2013 at 10:32
Molecular sieves?


So, being lucky enough to be a diabetic(T1) I need to use glucose test strips to determine my blood glucose levels. The manufacturer of the strips recently changed the small vials to include a plastic capsule filled with small beads, I immediately took it apart to squirrel away these beads in case they may be of use. My question is, what are they? I'm thinking some sort of molecular sieve (perhaps 4A?) but I'm not sure. There is sadly no MSDS or other information available from the manufacturer either. Given the ingredients, does anyone have a clue of what these things might be?


image.jpg - 138kB image.jpg - 112kB
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watson.fawkes
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[*] posted on 16-8-2013 at 10:39


Quote: Originally posted by Mailinmypocket  
Given the ingredients, does anyone have a clue of what these things might be?
It's a desiccant. The ingredients on the package have nothing to do with the beads.
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Mailinmypocket
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[*] posted on 16-8-2013 at 10:56


Hmm... Okay. I thought perhaps the glucose oxidase was oxygen sensitive or something. I wish I knew the composition of this stuff though.
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watson.fawkes
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[*] posted on 16-8-2013 at 11:11


Quote: Originally posted by Mailinmypocket  
I thought perhaps the glucose oxidase was oxygen sensitive or something. I wish I knew the composition of this stuff though.
It might also be an oxygen scavenger, too. The most common one I've seen, though, is finely divided elemental iron.

As to what the prills are, my first guess, just from the photo, was calcium chloride. If you want to get some indirect evidence, dry them in an oven and weigh. Put them in an "anti-desiccator" with a liquid water source to saturate the atmosphere inside. After a week, weigh them again. Since different desiccants have different capacities to sequester water, it'll give some idea.
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elementcollector1
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[*] posted on 18-8-2013 at 21:55


Does 'cryohol' (a mixture of dry ice and ethanol) still work if you replace the ethanol with isopropanol? I think it should, but mine failed to liquefy chlorine and it has me wondering.

EDIT: On that note, are there any alternative cryohol mixes? Dry ice is hard to come by where I am.

[Edited on 19-8-2013 by elementcollector1]




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[*] posted on 18-8-2013 at 22:07


you could try acetone if isopropanol doesn't work
It should though, according to wiki, it should reach -77'c

i would say LN2, but since dry ice is already hard to come by...
maybe you could try some form of mechanical cooling, but i doubt it will reach anywhere near dry ice would get you

http://en.wikipedia.org/wiki/List_of_cooling_baths

[Edited on 19-8-2013 by confused]
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[*] posted on 2-9-2013 at 19:47


Hello people,
I would like to know if an aromatic amide can in a one-pot reaction be halogenated to the N-haloamide and on the aromatic ring too?
To be specific, im talking about the hofmann rearrangement, which I want to use to make 4-chloroaniline from benzamide with TCCA in methanol, then rearrangement with lye.
I cant find any reason why it wont work if I would just use two times the stochiometric amount of TCCA and take two times more care during addition?

There are papers out there for the use of TCCA for N-chloroamides/hofmann rearrangement, there are papers out there for aromatic halogenation, but i cant find any thats stating this will not work, or why it is undesirable?
Or maybe its just rare someone wants to do such a thing?

I had some paper which proves my assumption it could be possible, it was stating ring-halogenation of an aromatic amide during a hofmann rearrangement. when hypochlorite solution was used in excess, as a side product.

Seems just logical it would work, as its for both cases an electrophilic chlorination.
Can someone tell me if I missed something?
Or is it indeed possible to make 4-Chloroaniline from Benzamide in one shot?
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[*] posted on 3-9-2013 at 00:23


If I recall correctly, you will need acidic conditions to chlorinate the benzene ring. I have some examples of NCS aromatic chlorination using sulphuric acid, or acetic acid, so I imagine that TCCA should need similar conditions. Please post the papers that you have on TCCA aromatic chlorination.
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[*] posted on 3-9-2013 at 04:42


Yes indeed, my reference use sulfuric acid as well as catalyst, forgot about the conditions needed, that wont do it.

But I got another ref, actually a bromination, with TCCA/NaBr to form tribromoisocyanuric acid/TBCA, in methanol.
Just TBCA in MeOH.
The attached reference for N-haloamide preparation uses just TCCA in MeOH.
How about now, that seems to work in theory?

Could the reaction of TBCA and benzamide lead to 4,N-dibromobenzamide?

I only post both relevant references, since i think i got them from here and dont want to waste polverones bandwidth;).

Attachment: jo00828a039.pdf (149kB)
This file has been downloaded 2147 times

Attachment: A New Regioselective Bromination of Activated Aromatic Rings.pdf (69kB)
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sonogashira
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[*] posted on 4-9-2013 at 03:27


Thanks. Here's a paper for 4-chlorination of N-acetylaniline with TCCA, if it's of any use.


Attachment: 4-chloroaniline.pdf (65kB)
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plante1999
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[*] posted on 9-9-2013 at 11:37


Does anyone have a good plating book (including chromium plating) to refer me to?

A download link would also be highly apprecied, (reference section or U2U).




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IrC
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[*] posted on 9-9-2013 at 13:18


Quote: Originally posted by plante1999  
Does anyone have a good plating book (including chromium plating) to refer me to?

A download link would also be highly apprecied, (reference section or U2U).


Old books yet still good. Much of the reason I find old books useful is they are free, they also cover making things used in the art, many of the procedures being old but proven are much easier for a home lab to build using available salvage.

http://archive.org/details/electroplatingtr00reet

http://archive.org/details/principleselect00fielgoog

http://archive.org/details/removalofcopperi00somm

http://archive.org/details/practicalelectro00brun

http://archive.org/details/completetreatise00langrich

http://archive.org/details/electrodepositio00languoft

http://archive.org/details/practicalelectro00bedeuoft

http://archive.org/details/acompletetreati00langgoog

http://archive.org/details/electroplatingma00harp

http://archive.org/details/structureofchrom93353kasp

http://archive.org/details/protectivevalueo13333blum

http://archive.org/details/acceleratedtests13451stra

http://archive.org/details/throwingpowerinc41271farb

http://archive.org/details/jresv43n2p101

http://archive.org/details/jresv46n6p472

http://archive.org/details/jstor-41326936

http://archive.org/details/cleaningelectrop02ream

http://archive.org/details/radiochemicalstu18rein

http://archive.org/details/practicalhandboo00trev

http://archive.org/details/bstj59-2-169

http://archive.org/details/cleaningelectrop00ream

http://archive.org/details/TheBrushElectricLightAndElectro-p...

http://archive.org/details/electroplatinga00wattgoog

http://archive.org/details/TheBrushElectricLightAndElectro-p...

http://archive.org/details/practicalelectro00bede

http://archive.org/details/electroplatingtr00barcrich

http://archive.org/details/electroplatingwi00hasl


[Edited on 9-10-2013 by IrC]




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[*] posted on 9-9-2013 at 17:28


What are the pros and cons of a 14/20 setup vs a 24/40 setup for the home chemist? As in learning the reactions, I know it would be fine. But what about a reasonable amount of reagent preparation, too small to be useful?



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[*] posted on 9-9-2013 at 17:32
methOH vs. methoxide


I've been trolling the forums for a couple years now, but this is obviously my first question: Why do many people discussing reagents abbreviate to methOH or methoxide? I can generally study the process occuring and figure whether it is methanol (methyl with hydroxyl) or a base like NaOH dissolved in methanol. But why would we want to default to these less exacting abbreviations in a discipline that usually requires exact naming (nitrite v. nitrate, nitrous oxide v. nitric oxide, or the many o- m- p-1- 2- etc variations of functional groups on a benzene ring)? Thanks so much for the forum. I'm finally able to get back to my chemistry interests after going through a mechanical eng detour.
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[*] posted on 9-9-2013 at 18:18


This is the first I've seen "methOH." MeOH is common and acceptable. Here are a couple references you may find helpful:

Standard Abbreviations and Acronyms (The Journal of Organic Chemistry)
Organic Chemistry Acronyms (UW-Madison Chem.)

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[*] posted on 12-9-2013 at 07:18
Question


Hi,
what causes the errosion of carbon electrodes during electrolysis of a copper sulfate solution?
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