The authors wish to acknowledge start-up funding from The University of Toledo, as well as funds from the American Chemical Society&#39;s Herman Frasch Foundation in partial support of this work. Mr. Thomas Kina is acknowledged for his assistance with developing a suitable pressure gauge for measuring the reaction pressures. Mr. Steve Modar is thanked for useful discussions.

CAUTION: 1) The following protocols have been deemed safe through repeated trials. However, caution should be exercised when sealing vials, throughout the reaction, and especially when opening the reactions, as inhomogeneity in the reaction vials may lead to equipment failure. Vials should be inspected for physical defects prior to use. Vials should be placed behind some form of blast shield or hood sash immediately after sealing to prevent incidents should the vials fail. 2) Although there is little chance for asphyxiat...

Using the van der Waals Equation of State, the approximate pressure of these systems can be calculated45
Eq. 1:&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;<img alt="Equation" src="/files/ftp_upload/58281/58281eq1.jpg" />
Under the conditions in Protocol 1, we can assume 26.3 mg of CO2 gives n =5.98 x 10-4 mols
<img alt="Equation 1b" src="/files/ftp_upload/5828...

The use of gaseous compounds in chemical reactions typically requires specialized equipment and procedures1,2. At bench scale, some gases can be added directly from a tank using a high pressure regulator3. An alternative method is to condense the gas under cryogenic conditions4,5. Although useful, these strategies require the use of specialized pressure reactors with valves, which can be cost prohibitive for running numerous reactions in parallel. This can therefore greatly slow the rate at which reaction screening can proceed. As a result, chemists have found it desirable to introduce these compounds using alternative methods. Ammonia can be added to reactions using different ammonium carboxylate salts, taking advantage of the weak equilibrium between these salts and free ammonia6. Transfer hydrogenation is an important strategy for reduction reactions of olefins, carbonyl, and nitro groups that circumvents the use of flammable hydrogen gas with compounds such as ammonium formate or hydrazine as carriers of H27. Another gas of interest in this area is carbon monoxide8 &#8211; CO can be generated in situ by liberation from metal carbonyl complexes9,10, or alternatively it can be generated by decarbonylation from sources such as formates and formamides11,12,13 or chloroform14,15.
One gas which has not enjoyed significant development in this respect is carbon dioxide16. One reason for this is that many transformations that involve CO2 also require high temperatures and pressures, and thus are automatically relegated to specialized reactors17,18. Recent efforts to develop more reactive catalysts, however, have facilitated running many of these reactions under atmospheric pressures of CO219,20,21,22. We recently discovered a reaction in which carbon dioxide could be used to mediate the &#947;-C(sp3)&#8211;H arylation of aliphatic amines23. This strategy was expected to combine the benefits of a static directing group approach including amide24,25,26,27,28, sulfonamide29,30,31,32, thiocarbonyl33,34, or hydrazone35-based directing groups (chemical robusticity), with the ease of a transient directing group (decreased step economy)36,37,38,39.
Although the reaction could occur under atmospheric pressure of CO2, the need for a Schlenk set-up to screen reactions proved prohibitively slow. Furthermore, increasing the pressure slightly led to improved reaction yields, but could not be easily achieved using a Schlenk line. We therefore sought an alternative strategy, and subsequently identified that dry ice could be easily used as a solid source of CO2 that could be added to a variety of reaction vessels to introduce the necessary amount of carbon dioxide to achieve moderate pressures (Figure 1). Though underutilized in synthesis, a similar strategy is fairly common as a method to generate liquid CO2 for chromatography and extraction applications40,41,42,43,44. Utilizing this strategy allowed our group to rapidly screen large numbers of reactions in parallel, while the ability to access moderate CO2 pressures of between 2-20 atmospheres were critical to improving the yields of the reactions. Under these conditions, both primary (1&#176;) and secondary (2&#176;) amines can be arylated with electron rich and electron poor aryl halides.

<table>
	<tbody>
		<tr>
			<td>7.5 mL Sample Vial with Screw Cap (Thermoset)</td>
			<td>Qorpak</td>
			<td>GLC-00984</td>
			<td>Can be reused.</td>
		</tr>
		<tr>
			<td>40 mL Sample Vial with Screw Cap (Thermoset)</td>
			<td>Qorpak</td>
			<td>GLC-01039</td>
			<td>Can be reused.</td>
		</tr>
		<tr>
			<td>Pressure Tube, #15 Thread, 7&#34; Long, 25.4 mm O.D.</td>
			<td>Ace Glass</td>
			<td>8648-06</td>
			<td>Can be reused.</td>
		</tr>
		<tr>
			<td>Pie-Block for 2 Dram Vials</td>
			<td>ChemGlass</td>
			<td>CG-1991-P14</td>
			<td>Can be reused.</td>
		</tr>
		<tr>
			<td>Pie-Block for 10 Dram Vials</td>
			<td>ChemGlass</td>
			<td>CG-1991-P12</td>
			<td>Can be reused.</td>
		</tr>
		<tr>
			<td>3.2 mm PTFE Disposable Stir Bars</td>
			<td>Fisher</td>
			<td>14-513-93</td>
			<td>Can be reused.</td>
		</tr>
		<tr>
			<td>C-MAG HS 7 Control Hotplate</td>
			<td>IKA</td>
			<td>20002695</td>
			<td></td>
		</tr>
		<tr>
			<td>Analytical Weighing Balance</td>
			<td>Sartorius</td>
			<td>QUINTIX2241S</td>
			<td></td>
		</tr>
		<tr>
			<td>Double-Ended Micro-Tapered Spatula</td>
			<td>Fisher Scientific</td>
			<td>21-401-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Hei-VAP Advantage - Hand Lift Model with G5 Dry Ice Condenser Rotary Evaporator</td>
			<td>Heidolph</td>
			<td>561-01500-00</td>
			<td></td>
		</tr>
		<tr>
			<td>Bump Trap 14/20 Joint</td>
			<td>ChemGlass</td>
			<td>CG-1322-01</td>
			<td></td>
		</tr>
		<tr>
			<td>tert-Amyl amine</td>
			<td>Alfa Aesar</td>
			<td>B24639-14</td>
			<td>Used as received.</td>
		</tr>
		<tr>
			<td>2-Methyl-N-(3-methylbenzyl)butan-2-amine</td>
			<td>N/A</td>
			<td>N/A</td>
			<td>Prepared from reductive amination of tert-amyl amine and 3-tolualdehyde in the presence of sodium borohydride in methanol.</td>
		</tr>
		<tr>
			<td>Palladium Acetate</td>
			<td>Chem-Impex International, Inc.</td>
			<td>4898</td>
			<td>Used as received.</td>
		</tr>
		<tr>
			<td>Silver Trifluoroacetate</td>
			<td>Oakwood Chemicals</td>
			<td>007271</td>
			<td>Used as received.</td>
		</tr>
		<tr>
			<td>Phenyl Iodide</td>
			<td>Oakwood Chemicals</td>
			<td>003461</td>
			<td>Used as received.</td>
		</tr>
		<tr>
			<td>Acetic Acid</td>
			<td>Fisher Chemical</td>
			<td>A38</td>
			<td>Used as received.</td>
		</tr>
		<tr>
			<td>1,1,1,3,3,3-Hexafluoroisopropanol</td>
			<td>Oakwood Chemicals</td>
			<td>003409</td>
			<td>Used as received.</td>
		</tr>
		<tr>
			<td>Deionized Water</td>
			<td></td>
			<td></td>
			<td>Obtained from in-house deionized water system.</td>
		</tr>
		<tr>
			<td>Dry Ice</td>
			<td>Carbonic Enterprises Dry Ice Inc.</td>
			<td></td>
			<td>Non-food grade dry ice.</td>
		</tr>
		<tr>
			<td>Concentrated Hydrochloric Acid</td>
			<td>Fisher Chemical</td>
			<td>A144SI</td>
			<td>Diluted to a 1.2 M solution prior to use.</td>
		</tr>
		<tr>
			<td>Diethyl Ether, Certified</td>
			<td>Fisher Chemical</td>
			<td>E138</td>
			<td>Used as received.</td>
		</tr>
		<tr>
			<td>Hexanes, Certified ACS</td>
			<td>Fisher Chemical</td>
			<td>H292</td>
			<td>Used as received.</td>
		</tr>
		<tr>
			<td>Saturated Ammonium Hydroxide</td>
			<td>Fisher Chemical</td>
			<td>A669</td>
			<td>Used as received.</td>
		</tr>
		<tr>
			<td>Dichloromethane</td>
			<td>Fisher Chemical</td>
			<td>D37</td>
			<td>Used as received.</td>
		</tr>
		<tr>
			<td>Sodium Sulfate, Anhydrous</td>
			<td>Oakwood Chemicals</td>
			<td>044702</td>
			<td>Used as received.</td>
		</tr>
		<tr>
			<td>250 mL Separatory Funnel</td>
			<td></td>
			<td></td>
			<td>Prepared in-house by staff glassblower.</td>
		</tr>
		<tr>
			<td>100 mL Round Bottom Flask</td>
			<td></td>
			<td></td>
			<td>Prepared in-house by staff glassblower.</td>
		</tr>
		<tr>
			<td>Scientific Disposable Funnel</td>
			<td>Caplugs</td>
			<td>2085136030</td>
			<td></td>
		</tr>
		<tr>
			<td>Borosilicate Glass Scintillation Vials, 20 mL</td>
			<td>Fisher Scientific</td>
			<td>03-337-15</td>
			<td></td>
		</tr>
		<tr>
			<td>5 mm O.D. Thin Walled Precision NMR Tubes</td>
			<td>Wilmad</td>
			<td>666000575</td>
			<td></td>
		</tr>
		<tr>
			<td>Chloroform-d</td>
			<td>Cambridge Isotope Laboratories, Inc.</td>
			<td>DLM-7</td>
			<td>Used as received.</td>
		</tr>
	</tbody>
</table>

achieving moderate pressures in sealed vessels using dry ice as a solid co2 source

Herein is presented a general strategy to perform reactions under mild to moderate CO2 pressures with dry ice. This technique obviates the need for specialized equipment to achieve modest pressures, and can even be used to achieve higher pressures in more specialized equipment and sturdier reaction vessels. At the end of the reaction, the vials can be easily depressurized by opening at room temperature. In the present example CO2 serves as both a putative directing group as well as a way to passivate amine substrates, thereby preventing oxidation during the organometallic reaction. In addition to being easily added, the directing group is also removed under vacuum, obviating the need for extensive purification to remove the directing group. This strategy allows the facile &#947;-C(sp3)-H arylation of aliphatic amines and has the potential to be applied to a variety of other amine-based reactions.

Following these protocols, it is possible to charge a reaction vial with an appropriate amount of carbon dioxide to achieve chemical reactions that require CO2 atmospheres. The pressure achieved in Step 1 is calculated to be approximately 3 atmospheres (see discussion for determination of this value), although due to partial solvation, the observed pressure is in the vicinity of 2 atmospheres at room temperature, and should be approximately 2.6 atmospheres under the reaction co...

Watch this Scientific Journal Video about Achieving Moderate Pressures in Sealed Vessels Using Dry Ice As a Solid CO2 Source at JoVE.com

Achieving Moderate Pressures in Sealed Vessels Using Dry Ice As a Solid CO2 Source

Here we present a protocol for performing reactions in simple reaction vessels under low-to-moderate pressures of CO2. The reactions can be performed in a variety of vessels simply by administering the carbon dioxide in the form of dry ice, without the need for costly or elaborate equipment or set-ups.

Achieving Moderate Pressures in Sealed Vessels Using Dry Ice As a Solid CO2 Source

Herein is presented a general strategy to perform reactions under mild to moderate CO2 pressures with dry ice. This technique obviates the need for ...